I get similar symptoms with Assassins Creed: Unity run under DXVK (with RADV).
The issue doesn't occur with LLVM8, and seems to be a regression in LLVM9 since
it worked fine with the last compile of LLVM9 I used (early May).

The workarounds don't work in my case (nodma, zerovram) so it might be a
separate issue.

Here's a screenshot of the glitch: https://imgur.com/aUgSjW1
See top left for most obvious example of it, although you can see blockiness
across the image.