Hi Michael,

That did the trick, many thanks!

I have not seen the crash you describe in the links; The script I think is just a warning, but in my case the behavior of the task bar is warning enough, I think.

Thanks again,

regards, Jogchum

It's hard to say for sure from reading the symptoms, but it reads a bit
like a problem I encountered.  

When plasma errors it sometimes silently switches to a software 
renderer.  If this has happend, check  ~/.config/kdeglobals and remove:

    [QtQuickRendererSettings]
    SceneGraphBackend=software

I've posted concerning this on KDE Discuss:
https://discuss.kde.org/t/on-error-kde6-x11-switched-to-the-software-renderer-how-to-reverse/13241?u=digitaltrails
https://discuss.kde.org/t/wayland-kwin-crashes-when-i-alt-tab/12730/10?u=digitaltrails

I run the script quoted in the second link that checks for this on each
login. 

Michael