all plasmoids (including taskbar) frozen for minutes

This bug usually occurred only once per session.
In one case I observed, that it occurred directly after returning from suspend mode.

In my current session, the freeze started (13 minutes
after boot and) 12 minutes after launch of the KDE session.
It lasted for 38 and a half minute.
Last time it went on for about 32 minutes.
I can observe these times easily because the clock of the
control bar gets frozen as well.

The freeze is complete, meaning that all plasmoids behave
as if they were images, no visual change, no reaction to actions (like
clicking, doubleclicking, …).
However, all the actions I do seem to be recorded by the plasma shell,
because they all get executed once the plasmoids come back to life again.

The duration of the freeze varied from ten to forty minutes.

Everything else is working normal, I can use the KWin features
like Alt+Tab to switch between open windows, Alt+F4 to close then