What is happening with vertex paint while SM6 (D3D12) is active?

Heya! I have some problem here
When i import mesh to UE5 with SM5 active vertex paint works as it should. Everything is fine except topology. UE5 changes it, ignores loopcuts and even moves vertexes so my modules stop connecting correctly without visible seams. It’s not a huge problem with big wall modules, but it could be crucial in the future.

Model is fully triangulated in blender before exporting

But when I turn SM6 on and restart engine my topology becomes fine but vertex paint just does not work. It happens with the same mesh and material instance

Every answer is appreciated!