I'm using alien's vtown KDE:

KDE Plasma: 5.20.4
KDE Frameworks: 5.77.0
Qt: 5.15.2

But I get a strange black line on the KDE Plasma panel (cf. "Black line on KDE Plasma panel"):
https://i.imgur.com/33E3Eq9.png

I've seen that black line show up when compositing gets disabled in KDE plasma 5. It seems that it can get disabled automatically if the compositor crashes (kwin I believe).

In plasma 5 check under "System Settings" > "Display and Monitor" > "Compositor" > "Enable compositor on startup". See if that is unchecked. Might also show a warning message in that window if the compositor recently crashed and disabled itself.

Alternatively you could check if your ~/.config/kwinrc has
Which I think is the same thing, but I've noticed it get toggled there too after a kwin crash, bringing the black line panel.

Edit: Also this is supposedly fixed in the upcoming frameworks 5.78, according to the bugfix list here https://pointieststick.com/2020/12/1...ll-the-things/

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