https://bugs.freedesktop.org/show_bug.cgi?id=72159
--- Comment #6 from octoploid octoploid@yandex.com --- (In reply to comment #5)
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).
I redirected the output of startx to a log file, but there's nothing interesting in there AFAICS.
(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?
Sorry, I just assumed that ssh would work because the machine still responds to SysRq input. I cannot test this ATM.