Comment # 2 on bug 939452 from Dominique Leuenberger

There have been quite some updates to GDM in Leap 42.1; can you please retest
this issue?

If the crash still appears, please enable DEBUG logging for gdm
(modify /etc/gdm/custom.conf and uncomment Debug=True which you can find in
there).
reeboot the system to enable the debugging, provoke the crash and then attach
the output of journalctl (for the respective boot)