Materials are heavier on GPU dependant on the Order they are applied?!

Hi,

I have made a simple Blueprint that spawns a grid of cubes with the grey default checker material. With a button press I trigger a flipflop, that exchanges the Material. After a while I noticed that whatever Material was on A input of the flipflop generated less load on the GPU than if it was on B Material.

PIE Launch
Swap grey to A - fast
swap a to b - slow
swap b to a - fast
swap a to b - slow
swap b to a - fast
period…

so I thought ok, apparently the first material that gets applied to a mesh is faster for whatever reason. However… I replaced the flipflop with a int so i could toggle through more materials

PIE Launch
Swap grey to 0 - fast
swap 1 to 2 - slow
swap 2 to 3 - fast
swap 3 to 4 - slow
swap 4 to 0 - fast
swap 0 to 1 - slow
swap 1 to 2 - fast
period…

If anybody has some clue what might be causing this, please comment (all materials are Material Instance with the same Parameter, sharing the same Parent)