Strange KDE rendering issues since updating

[Aragorn]

It’s not the driver, @philm. It’s a bug in kwin. I am seeing the same thing here on kernel 5.4 LTS with an Intel GPU. Please see this thread below…

The pop-up window cannot be redrawn,

Yes, I’ve run into this myself twice now since the update, i.e. certain graphical elements remaining on screen after they should have vanished. It’s a bug in the compositor, and restarting the compositor takes care of it.