It seems like this issue is maybe the same as this one associated with Intel driver here - https://bugs.freedesktop.org/show_bug.cgi?id=104536 But I may be misunderstanding. I will say that the AMDgpu drivers appear to have usability issues in Ubuntu 18.50, as my primary intent is gaming, and there is almost no possible configuration without major side effects. I did try amdgpu-pro, which caused a whole other set of issues. I also edit videos almost daily. So I notice issues immediately. Let me know what detail you require to proceed. I'm not sure where the issue could be, but mesa was mentioned in a similar bug report (https://bugs.launchpad.net/ubuntu/+source/gstreamer-vaapi/+bug/1767312).