i am waiting for new normal drivers since 20.4.2 version it was released 4/21/2020!!!!!!! 7 month ago!!!! because only these drivers don't crash in substance painter when i try to paint, or in render cycles in blender, i was trying every new version of drives and only THE 20.4.2 works properly, but with update blender 2.91 even the 20.4.2 can't run the cycles render, it crashed. Even PRO RENDER works really bad on my RX 5700 XT + Ryzen 7 3700X. New 20.11.3 is still crashing in substance.
I have the same type issue happening, not so much artifacts, but Substance Painter just stops responding when I try to do anything in it. After rolling back to 20.4.2 it no longer freezes, but that driver, like you said, doesn't work well with recent Blender and Cycles, not to mention the fan speed hangs forever regardless of tuning setting again. Plus a lot of the other early driver glitches with the RX 5700 XT are now back. I hope we get a fix for this rather inconvenient problem soon.