So, here's more proper working displacement test.. No bumpmapping just displaced geo...
Anyways that before, in my previous post happened when I lowered displacement ammount from 0,5 to 0,2. I fixed it by lowering to 0,1 and then back to 0,2. It happened only three times and so far only on this mesh, I played with displacement yesterday a LOT but this is the first time I saw it so I don't know what went wrong there...