diff --git a/src/__tests__/posthog-core.identify.js b/src/__tests__/posthog-core.identify.js
index f93858323..ee6b51c1c 100644
--- a/src/__tests__/posthog-core.identify.js
+++ b/src/__tests__/posthog-core.identify.js
@@ -7,7 +7,11 @@ jest.mock('../gdpr-utils', () => ({
 }))
 jest.mock('../decide')
 
-given('lib', () => Object.assign(new PostHog(), given.overrides))
+given('lib', () => {
+    const posthog = new PostHog()
+    posthog._init('testtoken', given.config, 'testhog')
+    return Object.assign(posthog, given.overrides)
+})
 
 describe('identify()', () => {
     given(
@@ -339,10 +343,6 @@ describe('reset()', () => {
         persistence: new PostHogPersistence(given.config),
     }))
 
-    beforeEach(() => {
-        given.lib._init('testtoken', given.config, 'testhog')
-    })
-
     it('clears persistence', () => {
         given.lib.persistence.register({ $enabled_feature_flags: { flag: 'variant', other: true } })
         expect(given.lib.persistence.props['$enabled_feature_flags']).toEqual({ flag: 'variant', other: true })
diff --git a/src/__tests__/posthog-core.js b/src/__tests__/posthog-core.js
index 967ed3c30..3bf2787df 100644
--- a/src/__tests__/posthog-core.js
+++ b/src/__tests__/posthog-core.js
@@ -16,7 +16,11 @@ jest.mock('../utils', () => ({
     document: { title: 'test' },
 }))
 
-given('lib', () => Object.assign(new PostHog(), given.overrides))
+given('lib', () => {
+    const posthog = new PostHog()
+    posthog._init('testtoken', given.config, 'testhog')
+    return Object.assign(posthog, given.overrides)
+})
 
 describe('capture()', () => {
     given('eventName', () => '$event')
@@ -29,6 +33,7 @@ describe('capture()', () => {
     given('config', () => ({
         property_blacklist: [],
         _onCapture: jest.fn(),
+        get_device_id: jest.fn().mockReturnValue('device-id'),
     }))
 
     given('overrides', () => ({
@@ -38,11 +43,13 @@ describe('capture()', () => {
         persistence: {
             remove_event_timer: jest.fn(),
             properties: jest.fn(),
+            update_config: jest.fn(),
         },
         sessionPersistence: {
             update_search_keyword: jest.fn(),
             update_campaign_params: jest.fn(),
             update_referrer_info: jest.fn(),
+            update_config: jest.fn(),
             properties: jest.fn(),
         },
         compression: {},
diff --git a/src/extensions/sessionrecording.ts b/src/extensions/sessionrecording.ts
index e52de6eff..1326a1ced 100644
--- a/src/extensions/sessionrecording.ts
+++ b/src/extensions/sessionrecording.ts
@@ -101,6 +101,15 @@ export class SessionRecording {
         })
     }
 
+    private getSessionManager() {
+        if (!this.instance.sessionManager) {
+            logger.error('Session recording started without valid sessionManager')
+            return
+        }
+
+        return this.instance.sessionManager
+    }
+
     startRecordingIfEnabled() {
         if (this.isRecordingEnabled()) {
             this.startCaptureAndTrySendingQueuedSnapshots()
@@ -185,14 +194,18 @@ export class SessionRecording {
     }
 
     private _startCapture() {
-        // According to the rrweb docs, rrweb is not supported on IE11 and below:
-        // "rrweb does not support IE11 and below because it uses the MutationObserver API which was supported by these browsers."
-        // https://github.com/rrweb-io/rrweb/blob/master/guide.md#compatibility-note
-        //
-        // However, MutationObserver does exist on IE11, it just doesn't work well and does not detect all changes.
-        // Instead, when we load "recorder.js", the first JS error is about "Object.assign" being undefined.
-        // Thus instead of MutationObserver, we look for this function and block recording if it's undefined.
+        const sessionManager = this.getSessionManager()
+        if (!sessionManager) {
+            return
+        }
         if (typeof Object.assign === 'undefined') {
+            // According to the rrweb docs, rrweb is not supported on IE11 and below:
+            // "rrweb does not support IE11 and below because it uses the MutationObserver API which was supported by these browsers."
+            // https://github.com/rrweb-io/rrweb/blob/master/guide.md#compatibility-note
+            //
+            // However, MutationObserver does exist on IE11, it just doesn't work well and does not detect all changes.
+            // Instead, when we load "recorder.js", the first JS error is about "Object.assign" being undefined.
+            // Thus instead of MutationObserver, we look for this function and block recording if it's undefined.
             return
         }
 
@@ -203,7 +216,7 @@ export class SessionRecording {
 
         this.captureStarted = true
         // We want to ensure the sessionManager is reset if necessary on load of the recorder
-        this.instance.sessionManager.checkAndGetSessionAndWindowId()
+        sessionManager.checkAndGetSessionAndWindowId()
 
         const recorderJS = this.getRecordingVersion() === 'v2' ? 'recorder-v2.js' : 'recorder.js'
 
@@ -231,6 +244,10 @@ export class SessionRecording {
     }
 
     private _updateWindowAndSessionIds(event: eventWithTime) {
+        const sessionManager = this.getSessionManager()
+        if (!sessionManager) {
+            return
+        }
         // Some recording events are triggered by non-user events (e.g. "X minutes ago" text updating on the screen).
         // We don't want to extend the session or trigger a new session in these cases. These events are designated by event
         // type -> incremental update, and source -> mutation.
@@ -258,7 +275,7 @@ export class SessionRecording {
         }
 
         // We only want to extend the session if it is an interactive event.
-        const { windowId, sessionId } = this.instance.sessionManager.checkAndGetSessionAndWindowId(
+        const { windowId, sessionId } = sessionManager.checkAndGetSessionAndWindowId(
             !isUserInteraction,
             event.timestamp
         )
diff --git a/src/posthog-core.ts b/src/posthog-core.ts
index edd056947..8d82ecb27 100644
--- a/src/posthog-core.ts
+++ b/src/posthog-core.ts
@@ -265,20 +265,22 @@ export class PostHog {
     __loaded_recorder_version: 'v1' | 'v2' | undefined // flag that keeps track of which version of recorder is loaded
     config: PostHogConfig
 
-    persistence: PostHogPersistence
     rateLimiter: RateLimiter
-    sessionPersistence: PostHogPersistence
-    sessionManager: SessionIdManager
     pageViewManager: PageViewManager
     featureFlags: PostHogFeatureFlags
     surveys: PostHogSurveys
     toolbar: Toolbar
-    sessionRecording: SessionRecording | undefined
-    webPerformance: WebPerformanceObserver | undefined
-    exceptionAutocapture: ExceptionObserver | undefined
 
-    _requestQueue: RequestQueue
-    _retryQueue: RetryQueue
+    // These are instance-specific state created after initialisation
+    persistence?: PostHogPersistence
+    sessionPersistence?: PostHogPersistence
+    sessionManager?: SessionIdManager
+
+    _requestQueue?: RequestQueue
+    _retryQueue?: RetryQueue
+    sessionRecording?: SessionRecording
+    webPerformance?: WebPerformanceObserver
+    exceptionAutocapture?: ExceptionObserver
 
     _triggered_notifs: any
     compression: Partial<Record<Compression, boolean>>
@@ -316,13 +318,6 @@ export class PostHog {
         this.surveys = new PostHogSurveys(this)
         this.rateLimiter = new RateLimiter()
 
-        // these are created in _init() after we have the config
-        this._requestQueue = undefined as any
-        this._retryQueue = undefined as any
-        this.persistence = undefined as any
-        this.sessionPersistence = undefined as any
-        this.sessionManager = undefined as any
-
         // NOTE: See the property definition for deprecation notice
         this.people = {
             set: (prop: string | Properties, to?: string, callback?: RequestCallback) => {
@@ -559,7 +554,7 @@ export class PostHog {
     _start_queue_if_opted_in(): void {
         if (!this.has_opted_out_capturing()) {
             if (this.get_config('request_batching')) {
-                this._requestQueue.poll()
+                this._requestQueue?.poll()
             }
         }
     }
@@ -622,8 +617,8 @@ export class PostHog {
             this.capture('$pageleave')
         }
 
-        this._requestQueue.unload()
-        this._retryQueue.unload()
+        this._requestQueue?.unload()
+        this._retryQueue?.unload()
     }
 
     _handle_queued_event(url: string, data: Record<string, any>, options?: XHROptions): void {
@@ -642,6 +637,9 @@ export class PostHog {
     }
 
     _send_request(url: string, data: Record<string, any>, options: CaptureOptions, callback?: RequestCallback): void {
+        if (!this.__loaded || !this._retryQueue) {
+            return
+        }
         if (this.rateLimiter.isRateLimited(options._batchKey)) {
             if (this.get_config('debug')) {
                 console.warn('[PostHog SendRequest] is quota limited. Dropping request.')
@@ -834,8 +832,8 @@ export class PostHog {
     ): CaptureResult | void {
         // While developing, a developer might purposefully _not_ call init(),
         // in this case, we would like capture to be a noop.
-        if (!this.__loaded) {
-            return
+        if (!this.__loaded || !this.sessionPersistence || !this._requestQueue) {
+            return logger.unintializedWarning('posthog.capture')
         }
 
         if (userOptedOut(this, false)) {
@@ -919,6 +917,10 @@ export class PostHog {
     }
 
     _calculate_event_properties(event_name: string, event_properties: Properties): Properties {
+        if (!this.persistence || !this.sessionPersistence) {
+            return event_properties
+        }
+
         // set defaults
         const start_timestamp = this.persistence.remove_event_timer(event_name)
         let properties = { ...event_properties }
@@ -1019,7 +1021,7 @@ export class PostHog {
      * @param {Number} [days] How many days since the user's last visit to store the super properties
      */
     register(properties: Properties, days?: number): void {
-        this.persistence.register(properties, days)
+        this.persistence?.register(properties, days)
     }
 
     /**
@@ -1046,7 +1048,7 @@ export class PostHog {
      * @param {Number} [days] How many days since the users last visit to store the super properties
      */
     register_once(properties: Properties, default_value?: Property, days?: number): void {
-        this.persistence.register_once(properties, default_value, days)
+        this.persistence?.register_once(properties, default_value, days)
     }
 
     /**
@@ -1073,7 +1075,7 @@ export class PostHog {
      * @param {Object} properties An associative array of properties to store about the user
      */
     register_for_session(properties: Properties): void {
-        this.sessionPersistence.register(properties)
+        this.sessionPersistence?.register(properties)
     }
 
     /**
@@ -1082,7 +1084,7 @@ export class PostHog {
      * @param {String} property The name of the super property to remove
      */
     unregister(property: string): void {
-        this.persistence.unregister(property)
+        this.persistence?.unregister(property)
     }
 
     /**
@@ -1091,7 +1093,7 @@ export class PostHog {
      * @param {String} property The name of the session super property to remove
      */
     unregister_for_session(property: string): void {
-        this.sessionPersistence.unregister(property)
+        this.sessionPersistence?.unregister(property)
     }
 
     _register_single(prop: string, value: Property) {
@@ -1191,7 +1193,7 @@ export class PostHog {
      * @returns {Function} A function that can be called to unsubscribe the listener. E.g. Used by useEffect when the component unmounts.
      */
     onSessionId(callback: SessionIdChangedCallback): () => void {
-        return this.sessionManager.onSessionId(callback)
+        return this.sessionManager?.onSessionId(callback) ?? (() => {})
     }
 
     /** Get list of all surveys. */
@@ -1251,6 +1253,9 @@ export class PostHog {
      * @param {Object} [userPropertiesToSetOnce] Optional: An associative array of properties to store about the user. If property is previously set, this does not override that value.
      */
     identify(new_distinct_id?: string, userPropertiesToSet?: Properties, userPropertiesToSetOnce?: Properties): void {
+        if (!this.__loaded || !this.persistence) {
+            return logger.unintializedWarning('posthog.identify')
+        }
         //if the new_distinct_id has not been set ignore the identify event
         if (!new_distinct_id) {
             console.error('Unique user id has not been set in posthog.identify')
@@ -1417,11 +1422,14 @@ export class PostHog {
      * Useful for clearing data when a user logs out.
      */
     reset(reset_device_id?: boolean): void {
+        if (!this.__loaded) {
+            return logger.unintializedWarning('posthog.reset')
+        }
         const device_id = this.get_property('$device_id')
-        this.persistence.clear()
-        this.sessionPersistence.clear()
-        this.persistence.set_user_state('anonymous')
-        this.sessionManager.resetSessionId()
+        this.persistence?.clear()
+        this.sessionPersistence?.clear()
+        this.persistence?.set_user_state('anonymous')
+        this.sessionManager?.resetSessionId()
         const uuid = this.get_config('get_device_id')(uuidv7())
         this.register_once(
             {
@@ -1464,7 +1472,7 @@ export class PostHog {
      */
 
     get_session_id(): string {
-        return this.sessionManager.checkAndGetSessionAndWindowId(true).sessionId
+        return this.sessionManager?.checkAndGetSessionAndWindowId(true).sessionId ?? ''
     }
 
     /**
@@ -1475,6 +1483,9 @@ export class PostHog {
      * @param options.timestampLookBack How many seconds to look back for the timestamp (defaults to 10)
      */
     get_session_replay_url(options?: { withTimestamp?: boolean; timestampLookBack?: number }): string {
+        if (!this.sessionManager) {
+            return ''
+        }
         const host = this.config.ui_host || this.config.api_host
         const { sessionId, sessionStartTimestamp } = this.sessionManager.checkAndGetSessionAndWindowId(true)
         let url = host + '/replay/' + sessionId
@@ -1681,12 +1692,9 @@ export class PostHog {
                 this.config.disable_persistence = this.config.disable_cookie
             }
 
-            if (this.persistence) {
-                this.persistence.update_config(this.config)
-            }
-            if (this.sessionPersistence) {
-                this.sessionPersistence.update_config(this.config)
-            }
+            this.persistence?.update_config(this.config)
+            this.sessionPersistence?.update_config(this.config)
+
             if (localStore.is_supported() && localStore.get('ph_debug') === 'true') {
                 this.config.debug = true
             }
@@ -1765,7 +1773,7 @@ export class PostHog {
      * @param {String} property_name The name of the super property you want to retrieve
      */
     get_property(property_name: string): Property | undefined {
-        return this.persistence['props'][property_name]
+        return this.persistence?.['props'][property_name]
     }
 
     /**
@@ -1788,7 +1796,7 @@ export class PostHog {
      * @param {String} property_name The name of the session super property you want to retrieve
      */
     getSessionProperty(property_name: string): Property | undefined {
-        return this.sessionPersistence['props'][property_name]
+        return this.sessionPersistence?.['props'][property_name]
     }
 
     toString(): string {
@@ -1851,11 +1859,11 @@ export class PostHog {
             return
         }
 
-        if (!this.get_config('disable_persistence') && this.persistence.disabled !== disabled) {
-            this.persistence.set_disabled(disabled)
+        if (!this.get_config('disable_persistence') && this.persistence?.disabled !== disabled) {
+            this.persistence?.set_disabled(disabled)
         }
-        if (!this.get_config('disable_persistence') && this.sessionPersistence.disabled !== disabled) {
-            this.sessionPersistence.set_disabled(disabled)
+        if (!this.get_config('disable_persistence') && this.sessionPersistence?.disabled !== disabled) {
+            this.sessionPersistence?.set_disabled(disabled)
         }
     }
 
diff --git a/src/posthog-featureflags.ts b/src/posthog-featureflags.ts
index 5b5b61ae6..0e3a40a0f 100644
--- a/src/posthog-featureflags.ts
+++ b/src/posthog-featureflags.ts
@@ -1,4 +1,4 @@
-import { _base64Encode, _entries, _extend } from './utils'
+import { _base64Encode, _entries, _extend, logger } from './utils'
 import { PostHog } from './posthog-core'
 import {
     DecideResponse,
@@ -225,7 +225,7 @@ export class PostHogFeatureFlags {
                 } else {
                     flagCallReported[key] = [flagReportValue]
                 }
-                this.instance.persistence.register({ [FLAG_CALL_REPORTED]: flagCallReported })
+                this.instance.persistence?.register({ [FLAG_CALL_REPORTED]: flagCallReported })
 
                 this.instance.capture('$feature_flag_called', { $feature_flag: key, $feature_flag_response: flagValue })
             }
@@ -265,6 +265,9 @@ export class PostHogFeatureFlags {
     }
 
     receivedFeatureFlags(response: Partial<DecideResponse>): void {
+        if (!this.instance.persistence) {
+            return
+        }
         this.instance.decideEndpointWasHit = true
         const currentFlags = this.getFlagVariants()
         const currentFlagPayloads = this.getFlagPayloads()
@@ -284,6 +287,10 @@ export class PostHogFeatureFlags {
      * @param {Object|Array|String} flags Flags to override with.
      */
     override(flags: boolean | string[] | Record<string, string | boolean>): void {
+        if (!this.instance.__loaded || !this.instance.persistence) {
+            return logger.unintializedWarning('posthog.feature_flags.override')
+        }
+
         this._override_warning = false
 
         if (flags === false) {
@@ -331,7 +338,7 @@ export class PostHogFeatureFlags {
         this.setPersonPropertiesForFlags(enrollmentPersonProp, false)
 
         const newFlags = { ...this.getFlagVariants(), [key]: isEnrolled }
-        this.instance.persistence.register({
+        this.instance.persistence?.register({
             [PERSISTENCE_ACTIVE_FEATURE_FLAGS]: Object.keys(filterActiveFeatureFlags(newFlags)),
             [ENABLED_FEATURE_FLAGS]: newFlags,
         })
@@ -350,7 +357,7 @@ export class PostHogFeatureFlags {
                 { method: 'GET' },
                 (response) => {
                     const earlyAccessFeatures = (response as EarlyAccessFeatureResponse).earlyAccessFeatures
-                    this.instance.persistence.register({ [PERSISTENCE_EARLY_ACCESS_FEATURES]: earlyAccessFeatures })
+                    this.instance.persistence?.register({ [PERSISTENCE_EARLY_ACCESS_FEATURES]: earlyAccessFeatures })
                     return callback(earlyAccessFeatures)
                 }
             )
diff --git a/src/posthog-surveys.ts b/src/posthog-surveys.ts
index c94bbbb3b..428068a9b 100644
--- a/src/posthog-surveys.ts
+++ b/src/posthog-surveys.ts
@@ -72,7 +72,7 @@ export class PostHogSurveys {
                 { method: 'GET' },
                 (response) => {
                     const surveys = response.surveys
-                    this.instance.persistence.register({ [SURVEYS]: surveys })
+                    this.instance.persistence?.register({ [SURVEYS]: surveys })
                     return callback(surveys)
                 }
             )
diff --git a/src/utils.ts b/src/utils.ts
index 2ee2ab003..012107fb6 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -77,6 +77,11 @@ const logger = {
             }
         }
     },
+    unintializedWarning: function (methodName: string): void {
+        if (Config.DEBUG && !_isUndefined(window.console) && window.console) {
+            logger.error(`[PostHog] You must initialize PostHog before calling ${methodName}`)
+        }
+    },
 }
 
 // UNDERSCORE