diff --git a/backend/services/validator_service.py b/backend/services/validator_service.py
index 80df580dc1..dc1f16dd79 100644
--- a/backend/services/validator_service.py
+++ b/backend/services/validator_service.py
@@ -1,6 +1,9 @@
 from flask import current_app
 from sqlalchemy import text
+from multiprocessing.dummy import Pool as ThreadPool
+import os
 
+from backend import db
 from backend.exceptions import NotFound
 from backend.models.dtos.mapping_dto import TaskDTOs
 from backend.models.dtos.stats_dto import Pagination
@@ -28,7 +31,6 @@
 from backend.services.stats_service import StatsService
 from backend.services.users.user_service import UserService
 from backend.services.mapping_service import MappingService
-import threading
 
 
 class ValidatorServiceError(Exception):
@@ -136,56 +138,65 @@ def _user_can_validate_task(user_id: int, mapped_by: int) -> bool:
             return False
 
     @staticmethod
-    def _process_tasks(
-        task_to_unlock, project_id, validated_dto, message_sent_to, dtos
-    ):
-        task = task_to_unlock["task"]
-
-        if task_to_unlock["comment"]:
-            # Parses comment to see if any users have been @'d
-            MessageService.send_message_after_comment(
-                validated_dto.user_id,
-                task_to_unlock["comment"],
-                task.id,
-                validated_dto.project_id,
-            )
-        if (
-            task_to_unlock["new_state"] == TaskStatus.VALIDATED
-            or task_to_unlock["new_state"] == TaskStatus.INVALIDATED
-        ):
-            # All mappers get a notification if their task has been validated or invalidated.
-            # Only once if multiple tasks mapped
-            if task.mapped_by not in message_sent_to:
-                MessageService.send_message_after_validation(
-                    task_to_unlock["new_state"],
+    def _process_tasks(args):
+        (
+            app_context,
+            task_to_unlock,
+            project_id,
+            validated_dto,
+            message_sent_to,
+            dtos,
+        ) = args
+        with app_context:
+            task = task_to_unlock["task"]
+
+            if task_to_unlock["comment"]:
+                # Parses comment to see if any users have been @'d
+                MessageService.send_message_after_comment(
                     validated_dto.user_id,
-                    task.mapped_by,
+                    task_to_unlock["comment"],
                     task.id,
                     validated_dto.project_id,
                 )
-                message_sent_to.append(task.mapped_by)
+            if (
+                task_to_unlock["new_state"] == TaskStatus.VALIDATED
+                or task_to_unlock["new_state"] == TaskStatus.INVALIDATED
+            ):
+                # All mappers get a notification if their task has been validated or invalidated.
+                # Only once if multiple tasks mapped
+                if task.mapped_by not in message_sent_to:
+                    MessageService.send_message_after_validation(
+                        task_to_unlock["new_state"],
+                        validated_dto.user_id,
+                        task.mapped_by,
+                        task.id,
+                        validated_dto.project_id,
+                    )
+                    message_sent_to.append(task.mapped_by)
 
-            if task_to_unlock["new_state"] == TaskStatus.VALIDATED:
-                # Set last_validation_date for the mapper to current date
-                task.mapper.last_validation_date = timestamp()
+                if task_to_unlock["new_state"] == TaskStatus.VALIDATED:
+                    # Set last_validation_date for the mapper to current date
+                    task.mapper.last_validation_date = timestamp()
 
-        # Update stats if user setting task to a different state from previous state
-        prev_status = TaskHistory.get_last_status(project_id, task.id)
-        if prev_status != task_to_unlock["new_state"]:
-            StatsService.update_stats_after_task_state_change(
-                validated_dto.project_id,
+            # Update stats if user setting task to a different state from previous state
+            prev_status = TaskHistory.get_last_status(project_id, task.id)
+            if prev_status != task_to_unlock["new_state"]:
+                StatsService.update_stats_after_task_state_change(
+                    validated_dto.project_id,
+                    validated_dto.user_id,
+                    prev_status,
+                    task_to_unlock["new_state"],
+                )
+            task_mapping_issues = ValidatorService.get_task_mapping_issues(
+                task_to_unlock
+            )
+            task.unlock_task(
                 validated_dto.user_id,
-                prev_status,
                 task_to_unlock["new_state"],
+                task_to_unlock["comment"],
+                issues=task_mapping_issues,
             )
-        task_mapping_issues = ValidatorService.get_task_mapping_issues(task_to_unlock)
-        task.unlock_task(
-            validated_dto.user_id,
-            task_to_unlock["new_state"],
-            task_to_unlock["comment"],
-            issues=task_mapping_issues,
-        )
-        dtos.append(task.as_dto_with_instructions(validated_dto.preferred_locale))
+            dtos.append(task.as_dto_with_instructions(validated_dto.preferred_locale))
 
     @staticmethod
     def unlock_tasks_after_validation(
@@ -205,17 +216,29 @@ def unlock_tasks_after_validation(
         # Unlock all tasks
         dtos = []
         message_sent_to = []
-        threads = []
+        args_list = []
         for task_to_unlock in tasks_to_unlock:
-            thread = threading.Thread(
-                target=ValidatorService._process_tasks,
-                args=(task_to_unlock, project_id, validated_dto, message_sent_to, dtos),
+            args = (
+                current_app.app_context(),
+                task_to_unlock,
+                project_id,
+                validated_dto,
+                message_sent_to,
+                dtos,
             )
-            threads.append(thread)
-            thread.start()
+            args_list.append(args)
+
+        # Create a pool and Process the tasks in parallel
+        pool = ThreadPool(os.cpu_count())
+        pool.map(ValidatorService._process_tasks, args_list)
+
+        # Close the pool and wait for the threads to finish
+        pool.close()
+        pool.join()
+        db.session.commit()
+
+        # Send email on project progress
         ProjectService.send_email_on_project_progress(validated_dto.project_id)
-        for thread in threads:
-            thread.join()
         task_dtos = TaskDTOs()
         task_dtos.tasks = dtos