I just got a brand new amd radeon 6800 xt and i'm having this problem everytime I add displacement in my material nodes. I'm using cycles render. In preview it looks nice, the problem appears in the final image result. When I render using only CPU it turns out nice. With my previous gtx 1660 i've never had this issue. All drivers are updated and I've tried several blender versions without success...
I have a cheap class Amd GPU (RX570) also having a lot of trouble in rendering with cycles.
I think AMD developers need to work extra hard so that their GPU can run smoothly supported by good program compatibility, such as drivers or others.
For now, I often experience problems with cycles when using the GPU. and when i want to try radeon prorender .. i also have trouble. Until now no one wants to help me.
Hopefully we can find a solution here.