VRAM overflow despite using medium textures.

For me it starts in act 2 (act 1 was just fine).
First some textures disappear and then weird flickering starts.
I have 6gb on my videocard and your minimum system requirements say that 3gb should be enough.
I would also point out that this is first time I see this and I was playing since EA release.
Playing with vulkan renderer, in case it matters.