Created attachment 139715 [details]
dmesg

Gigabyte X470-AORUS-ULTRA-GAMING board with AMD Ryzen 5 2400g APU, Fedora 28,
git MESA, git AMDGPU; box was migrated today from AMD A10-5800 based solution.

I found these in xorg.log:

[  1894.583] (WW) AMDGPU(0): flip queue failed: Cannot allocate memory
[  1894.583] (WW) AMDGPU(0): Page flip failed: Cannot allocate memory
[  1894.583] (EE) AMDGPU(0): present flip failed
[  1894.594] (WW) AMDGPU(0): flip queue failed in amdgpu_scanout_flip: Cannot
allocate memory, TearFree inactive until next modeset