12.3: KDE panel reaction to clicks lags significantly

when clicking on an icon in the KDE panel on 12.3, the panel takes up to more than 10 seconds to react.
other actions on the desktop, that don’t involve the panel (eg. selecting or moving a window) work immediately.

after a logging out and in again, this problem is gone at first: the panel reacts immediately.
the reaction time of the panel however then slowly decreases again. within a few hours the reaction of the panel again takes more than 10 seconds.

I don’t remember having made made changes to the panel before this behaviour started. maybe an installation of updated packages via yast.

Does anyone have a hint on how to solve that or where to start to search for the cause?