Created attachment 145897 [details]
screenshot when problem happens

SUMMARY
While it works mostly OK in 5.23.5, with 5.23.90 plasma I always get plasma show the wrong placement after plugin an external screen.


STEPS TO REPRODUCE
1. plug in external monitor

OBSERVED RESULT
Panel that previously on the laptop screen is moved to the external monitor
external monitor desktop is black. kquitapp5 plasmashell and restart plasmashell can make it work again.

EXPECTED RESULT
Plasma have panel in the right place and show desktop correctly.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.23.90 
(available in About System)
KDE Plasma Version: 5.23.90
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
relevant supportInformation in KWin
Screens
=======
Multi-Head: no
Active screen follows mouse:  yes
Number of Screens: 2

Screen 0:
---------
Name: eDP-1
Geometry: 0,0,1536x864
Scale: 1.25
Refresh Rate: 144028
Adaptive Sync: incapable
Screen 1:
---------
Name: DP-1
Geometry: 1536,0,2048x1152
Scale: 1.25
Refresh Rate: 59951
Adaptive Sync: incapable