Comment # 22 on bug 1013200 from Patrick Schaaf

Situation after reinstall:

The initial boot after installing, without update repositories active yet, had
a plymouth coredump, but sddm-greeter did NOT coredump, and the graphical login
was shown.

I then activated the update repositories, zypper dupped, and rebooted. Voila,
the issue occurs again. Disabled plymouth once more, issue persists.

I now built myself an OnBootSec=45 systemd timer unit initiating "systemctl
restart --no-block display-manager" - that works. Ugh...