Comment # 2 on bug 1084629 from Fabian Vogt

(In reply to Marius Kittler from comment #1)
> So this is clearly an SDDM issue then.

Or Mesa, or Qt, or graphics driver, or X...

Does this issue still exist?

> I'm also recently experiencing a similar (maybe the same) issue. In my case
> SDDM also just hangs leaving me with a black screen. Maybe it is just very
> slow.
> 
> When I switch to another tty I can restart SDDM via `systemctl restart
> display-manager` which sometimes helps. If not, I currently just stop the
> hanging display manager and start the X/Plasma session myself using
> `startx`. This always works - so the X server can not be the problem.
> 
> I made another observation: When opening the SDDM configuration in
> systemsettings5 it takes very very long to load (but it finally shows up).

That's interesting. It opens near instantly for me.
It might be QML related, what happens with LIBGL_ALWAYS_SOFTWARE=1 kcmshell5
kcm_sddm?

> 
> Unfortunately the journal of SDDM or the systemsettings5 output do not
> contain any useful information like error messages.
> 
> Maybe it helps to remove the cache here, too. The slowly loading
> systemsettings5 keeps loading slow, also with the cache removed. I'll try to
> restart later to check whether it at least helps for SDDM itself.