Comment # 8 on bug 970598 from Wolfgang Bauer

(In reply to George Olson from comment #7)
> I am upgrading the severity and the priority to get this fixed ASAP.

You are not supposed to change the priority, unless you are willing to work on
this yourself (but in this case, please assign the bug report to yourself).

Regarding the problem:
The bug report you mention (that's fixed in 5.6) is about kwin not being able
to restart after a crash because it detects that it is already running (the
crashed  process that is captured by drkonqi and therefore frozen).
And that's what's fixed, it should restart itself now after a crash, so the
graphics would not be frozen.

I had a look, and the fix should apply as-is to 5.5 as well, so an update would
be no problem.

It doesn't fix the actual crashes though, and with your information it is
impossible to do anything about that anyway. We'd need a backtrace of a crash,
which you can get as described here: https://community.kde.org/KWin/Debugging

It would be preferable though if you reported your crashes upstream to the KDE
developers (including a backtrace).
Of course drkonqi (the crash dialog) would make that slightly easier... ;-)

Although you probably should try 5.6 before that as the crashes might have been
fixed already too.
You can also install 5.6 from the KDE:Frameworks5 repo (needs KDE:Qt5 as well),
where it is available since weeks.
See https://en.opensuse.org/SDB:KDE_repositories#KDE_Frameworks_5_.26_Plasma_5


Btw, I don't see kwin_x11 crashing here, on neither of 2 different systems (one
radeon, one intel), so this might not be as general a problem as you think.
I do know that some people see the same with certain versions of the nvidia
driver.
One particular thing that can cause such crashes I know of are certain window
decorations (Plastik e.g. or anything using Aurorae, although I have no problem
with that either). So if you changed that, try switching back to breeze.