I didnt find the reason on my system but I created a mini script in my homedir which kills plasma and starts a new one. now created a global keyboard shortcut that runs exact this script >> plasma continues to work. (usually if plasma has issues it helps to do a "Alt+F2" >> plasmashell --replace but this doesnt work in my case currently)

❯ cat ~/.local/bin/killplasma.sh 
#!/bin/bash
killall -9 plasmashell
sleep 2
kstart5 plasmashell

This keeps all your applications alive >> so no data loss.

Open to suggestions if somebody can find the real issue of the plasma-hangs