Comment # 12 on bug 107928 from Michel Dänzer

(In reply to Matthew Vaughn from comment #11)
> Downgrading from x11-drivers/xf86-video-amdgpu-18.1.0 to
> x11-drivers/xf86-video-amdgpu-18.0.1 has prevented the issue from occurring
> on my system.

Can you bisect xf86-video-amdgpu?