Periodic boundary conditions cant be applied because assembly changes sparsity pattern?

ErrorMWE.jl

using Ferrite


function assemble_element!(Me :: Matrix, Ke::Matrix, cellvalues::CellValues, q :: Ferrite.Vec{2})
	n_basefuncs = getnbasefunctions(cellvalues)
	# Reset to 0
	fill!(Me, 0)
	fill!(Ke, 0)
	# Loop over quadrature points
	for q_point in 1:getnquadpoints(cellvalues)
		 # Get the quadrature weight
		 dΩ = getdetJdV(cellvalues, q_point)
		 # Loop over test shape functions
		 for i in 1:n_basefuncs
			  v  = shape_value(cellvalues, q_point, i)
			  ∇v = shape_gradient(cellvalues, q_point, i)
			  # Loop over trial shape functions
			  for j in 1:n_basefuncs
					u = shape_value(cellvalues, q_point, j)
					∇u = shape_gradient(cellvalues, q_point, j)
					# Add contribution to Ke
					Me[i, j] += u * v * dΩ
					Ke[i, j] += (q ⋅ ∇u) * v * dΩ
			  end
		 end
	end
	return Me, Ke
end

function assemble_global!(cellvalues, dh, q::Ferrite.Vec{2})
	n_basefns = getnbasefunctions(cellvalues)
	M = allocate_matrix(dh)
	K = allocate_matrix(dh)
	Me = zeros(n_basefns, n_basefns)
	Ke = zeros(n_basefns, n_basefns)
	M_ass = start_assemble(M)
	K_ass = start_assemble(K)
	for cell in CellIterator(dh)
		reinit!(cellvalues, cell)
		assemble_element!(Me, Ke, cellvalues, q)
		assemble!(M_ass, celldofs(cell), Me)
		assemble!(K_ass, celldofs(cell), Ke)
	end
	return M, K
end

grid = generate_grid(Quadrilateral, (100, 1)) # 1d mesh didn't work

ip = Lagrange{RefQuadrilateral, 1}()
dh = DofHandler(grid)
add!(dh, :c, ip)
close!(dh)
cellvalues = CellValues(QuadratureRule{RefQuadrilateral}(2), ip)

ch = ConstraintHandler(dh)
mapping = collect_periodic_facets(grid, "left", "right", (x) -> x - Ferrite.Vec{2}((2.0, 0.0)))
pdbc = PeriodicDirichlet(:c, mapping, [1,])
add!(ch, pdbc)
close!(ch)




# this works
B = allocate_matrix(dh)
_ = get_rhs_data(ch, B)
apply!(B, ch)






# this doesnt 
M, K = assemble_global!(cellvalues, dh, +Ferrite.Vec{2}((1.0, 0)))
Δt = 0.01
A = M .+ (Δt .* K)
rhs_data = get_rhs_data(ch, A)
apply!(A, ch)