Comment # 17 on bug 1122807 from Fabian Vogt

(In reply to chris reid from comment #16)
> Created attachment 795382 [details]
> journctl output
> 
> There is some extra debug I have added to xrandr library
> You will see it in the output
> I added it in the hope of entering a function and not leaving it, to find
> the problem.
> toKScreenScreen     //is entering function toKScreenScreen
> toKScreenScreenEOF  // is existing function toKScreenScreen
> But again there was nothing useful,
> And it did not change the bug.

I don't see any crash in there, is anything useful in
~/.local/share/sddm./xorg-session.log or /var/log/Xorg.0.log(.old)?