It had been a while since I performed an update (bad on me) so it was a rather large package set. But after upgrading GDM/Gnome became completely unusable. Everything was very slow to react and the mouse would track for a fraction of a second and the pause for a while.

I'm not sure if it was the actual problem but downgrading gnome-shell "fixed" the problem enough that I now have a usable GUI, but only if I run startx from the command line. 

Trying to use journalctl from a 80 column CLI to figure out the problem was an exercise in futility... The lines are just way too long.

I tried booting the previous kernel to no avail so it doesn't look like that was the core problem.

gnome-shell core dumped in my last boot but not in the previous two so...

The only consistent error has been:

Mar 20 17:50:22 hobbes.localdomain kernel: [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CRTC:32:crtc-0] flip_done timed out
Mar 20 17:50:32 hobbes.localdomain kernel: [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [PLANE:30:plane-0] flip_done timed o
Mar 20 17:50:42 hobbes.localdomain kernel: [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [CRTC:35:crtc-1] flip_done timed out
Mar 20 17:50:52 hobbes.localdomain kernel: [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR* [PLANE:33:plane-2] flip_done timed o

I am running the nvidia binary drivers but there has only been minor updates and I've now updated to the new version in updates-testing (390.40) did not help.

Ideas?

Thanks,
Richard