This issue must have come with 4.14.1, as the uptime of the laptop was around 7 days. On a A275 with amdgpu everything is garbled below the top panel when compositing enabled.
Created attachment 9754
Fixed by switching back to glx.
That'd be a driver bug, can you please file an issue upstream at https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues
Thanks, filed a bug report: https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/10
Olivier Fourdan referenced this bugreport in commit 7c00911a556c27c57c9f719c12cfda967016dc28
compositor: Do not prefer XPresent on AMD hardware
For now, I just reverted to GLX by default in xfwm4, until Michel's fix lands upstream.