Fwd: Taskbar and Plasma 5.20.4

[MERLIN Philippe <phil-deb1.merlin@laposte.net>]

Hello,
My system is an AMD64 Sid, since the Plasma migration to 5.20.4 I have 
problems with my taskbar, for example if I click on the Firefox icon I no 
longer see the window showing all the sessions Firefox open, it must be 
recognized that I often have more than 10 sessions open simultaneously, now to 
access a particular session I have to click on the Firefox icon and I see all 
the sessions scrolling. Another oddity some sessions are no longer visible 
only the title appears, impossible to see these sessions. This problem does 
not only concern Firefox, Dolphin, Konsole ...
I would like to go back to normal operation, is there a way out?
Cheers.
Philippe Merlin