EDIT (yesterday only the 3th, today the 1st and 2nd)

in KDE Neon, after upgrade to Plasma 5.17

1. After login: black screen (not always, sometimes: 1 on 3 or so)
2. Resuming from lockscreen: crash (once, so far)
3. I can't see the triangle icons (expand/compress) i.g. in Thunderbird and in autokey, in any user. I see them only with mouse over.

EDIT
Maybe these problems depend on the same cause?
However in virtualbox Neon 5.17 has the 3th problem, but not the first and the second (many login tests: always ok).

Can you help me?
Thanks

Yeah me too, and I found this in journal:
Oct 18 06:45:51 desktop kernel: plasmashell[2811]: segfault at 5618a3fabf88 ip 00007f6cf3014162 sp 00007ffd9664eb20 error 4 in libQt5Core.so.5.13.1[7f6cf2dbd000+53c000]
Oct 18 06:45:51 desktop kernel: Code: 0f 85 22 03 00 00 66 90 48 63 eb 48 8b 74 24 58 48 8d 3c ad 00 00 00 00 48 8d 14 38 48 03 50 10 48 89 7c 24 48 48 8b 7c 24 10 <8b> 02 89 84 24 80 00 00 00 e8 90 08 ed ff 48 8b 6c 24 28 83 c3 01
Strangely, I can launch plasmashell from cmdline successfully.

Maybe the problem of blank screen after login is the slideshow wallpaper: I have to do some further test.
EDIT
Yes, so far it seems that the problem: a random desktop wallpaper slideshow.

That would likely be me too..I bet I'm running variety on that partition. I'll try it this afternoon, when I reboot.

My plasma is falling. Black screen. Helps $ plasmashell