Comment 34 for bug 2003339

Not sure how much of this is just a coincidence or if it is actually related:
Before I had the "KWin just quits" issue I had problems where KWin sometimes just "forgot to update a window", meaning a window starts flickering between some old window states instead of rendering new ones. The issue was "fixable" by toggling compositing off and on again (using Ctrl+Shift+F12 by default I think). I had that issue for a few years but never really investigated as just pressing the keys was an easy work around for me. How often this happened varied from once every few days to multiple times an hour, though subjectively it was occurring more often lately than a year ago.

At the beginning of November I changed my default browser from Chrome to Firefox and that issue didn't happen anymore for a few days so I thought maybe it was a wired interaction between Chrome and KWin. Then this issue started happening.

What both issues/behaviors have in common is that I noticed that usually there are notifications being shown when it happens. The "old issue" with stuck rendering showed the notifications just fine and also still updated a small (maybe 30 px?) region around the notification popup. With this issue I saw a notification pop up appear as a black rectangle and then KWin crashing (and sometimes also Plasmashell hanging after the KWin restart).