Comment # 1 on bug 932628 from Wolfgang Bauer

I suspect this is related to your newer bug#932787 , where you mention the same
for a regular GNOME session too.

Marking as duplicate, I don't think this is a KDE issue anyway.

Maybe some problem because gdm runs on Wayland?
Can you login to IceWM? (might be an Xorg graphics driver problem too I think)

*** This bug has been marked as a duplicate of bug 932787 ***