diff --git a/src/derivative_utils.jl b/src/derivative_utils.jl
index 67333bdc3..15167d650 100644
--- a/src/derivative_utils.jl
+++ b/src/derivative_utils.jl
@@ -17,6 +17,8 @@ function calc_H_EK0!(H, integ, cache)
     @unpack f = integ
     @unpack d, ddu, E1, E2 = cache
 
+    return nothing
+
     if f isa DynamicalODEFunction
         @assert f.mass_matrix === I
         H .= E2
diff --git a/src/fast_linalg.jl b/src/fast_linalg.jl
index 4975612de..1a3d9b389 100644
--- a/src/fast_linalg.jl
+++ b/src/fast_linalg.jl
@@ -13,21 +13,9 @@ _matmul!(C, A, B)
 _matmul!(C, A, B) = mul!(C, A, B)
 _matmul!(C, A, B, a, b) = mul!(C, A, B, a, b)
 # Some special cases
-_matmul!(
-    C::AbstractMatrix{T},
-    A::AbstractMatrix{T},
-    B::Diagonal{T},
-) where {T<:LinearAlgebra.BlasFloat} = (@.. C = A * B.diag')
-_matmul!(
-    C::AbstractMatrix{T},
-    A::Diagonal{T},
-    B::AbstractMatrix{T},
-) where {T<:LinearAlgebra.BlasFloat} = (@.. C = A.diag * B)
-_matmul!(
-    C::AbstractMatrix{T},
-    A::Diagonal{T},
-    B::Diagonal{T},
-) where {T<:LinearAlgebra.BlasFloat} = @.. C = A * B
+_matmul!(C::AbstractMatrix, A::AbstractMatrix, B::Diagonal) = (@.. C = A * B.diag')
+_matmul!(C::AbstractMatrix, A::Diagonal, B::AbstractMatrix) = (@.. C = A.diag * B)
+_matmul!(C::AbstractMatrix, A::Diagonal, B::Diagonal) = @.. C = A * B
 _matmul!(
     C::AbstractMatrix{T},
     A::AbstractVecOrMat{T},
diff --git a/src/initialization/common.jl b/src/initialization/common.jl
index 884dfac0d..1b9941849 100644
--- a/src/initialization/common.jl
+++ b/src/initialization/common.jl
@@ -98,10 +98,10 @@ function condition_on!(
     _matmul!(x.μ, K, datadiff, 1, 1)
 
     D = length(x.μ)
-    _matmul!(Mcache, K, H, -1, 0)
-    @inbounds @simd ivdep for i in 1:D
-        Mcache[i, i] += 1
-    end
+    # _matmul!(Mcache, K, H, -1, 0)
+    # @inbounds @simd ivdep for i in 1:D
+    #     Mcache[i, i] += 1
+    # end
 
     d, q1 = size(H.A, 1), size(x.Σ.R.B, 1)
     _I = kronecker(I(d), I(q1))
diff --git a/src/perform_step.jl b/src/perform_step.jl
index dfd3aeb87..af240f73b 100644
--- a/src/perform_step.jl
+++ b/src/perform_step.jl
@@ -229,11 +229,12 @@ function estimate_errors!(cache::AbstractODEFilterCache)
 
         if H isa Kronecker.KroneckerProduct
             error_estimate = ones(d)
-            error_estimate .*= (Qh.R.B * H.B')[1]^2
+            error_estimate .*= sum(abs2, Qh.R.B * H.B')
             # error_estimate = view(cache.tmp, 1:d)
             # sum!(abs2, error_estimate', view(R, :, 1:d))
             error_estimate .*= local_diffusion
             error_estimate .= sqrt.(error_estimate)
+            return error_estimate
         else
 
         _matmul!(R, Qh.R, H')
diff --git a/src/priors/iwp.jl b/src/priors/iwp.jl
index c3a8950fd..252589e9d 100644
--- a/src/priors/iwp.jl
+++ b/src/priors/iwp.jl
@@ -120,9 +120,7 @@ function make_transition_matrices!(cache, prior::IWP, dt)
     make_preconditioners!(cache, dt)
     # A, Q = preconditioned_discretize(p) # not necessary since it's dt-independent
     # Ah = PI * A * P
-    # @.. Ah = PI.diag * A * P.diag'
-    Ah.B .= PI.B * A.B * P.B
+    @.. Ah.B = PI.B.diag * A.B * P.B.diag'
     # X_A_Xt!(Qh, Q, PI)
-    # @.. Qh.R = Q.R * PI.diag
-    Qh.R.B .= Q.R.B * PI.B
+    @.. Qh.R.B = Q.R.B * PI.B.diag
 end
diff --git a/src/projection.jl b/src/projection.jl
index 8d26f5c0a..13f10a549 100644
--- a/src/projection.jl
+++ b/src/projection.jl
@@ -1,6 +1,10 @@
 function projection(d::Integer, q::Integer, ::Type{elType}=typeof(1.0)) where {elType}
     Id = _I(d)
-    Proj(deriv) = kronecker(Id, [i == (deriv + 1) ? 1 : 0 for i in 1:q+1]')
+    Proj(deriv) = begin
+        e_i = zeros(q+1, 1)
+        e_i[deriv+1] = 1
+        kronecker(Id, e_i')
+    end
 
     # Slightly faster version of the above:
     # D = d * (q + 1)