https://bugs.freedesktop.org/show_bug.cgi?id=72159

--- Comment #5 from Michel Dänzer michel@daenzer.net --- Looks like the X server may not shut down cleanly. Is there something interesting in its stderr output? You may find it in the display manager log file(s).

(In reply to comment #4)

...

Can you still log in via ssh at that point?

Yes.

What happens if you try starting X again or switching VTs using chvt from ssh?