Found out what's causing it. I've been trying to track this down for a while.
It's caused by the SSAO depth + normals, and digging a bit deeper, the Skin Shader depth-normal pass doesn't like reusing the diffuse map sampler in 2021.x+, which causes an error and so this dithering effect in 2021.x and above. The skin shaders can use more than 16 textures and so need to re-use texture samplers, only the depth normal pass seems to be picky about which samplers it can use.
Edit: In fact it looks like all the Amplify shaders also need to be recompiled for URP 12 as it uses a different template.
Edited
2 Years Ago by
Victor.Soupday