Created attachment 125288 [details]
Illustration of the problem

SUMMARY
I have two displays:
DVI-0 1280×1024
DVI-1 1920×1080 — main display
The first one placed on the left from the second.

Please look at the image attached.

STEPS TO REPRODUCE
1. Add widgets to desktop on display connected via DVI-1 (where green frame on the illustration)
2. Log off
3. Log in

OBSERVED RESULT
On the illustration: widgets now are moved to the left from their original positions (yellow frame)

EXPECTED RESULT
Widgets are stay where they was before log off (green frame)

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20200117
KDE Plasma Version: 5.17.5
KDE Frameworks Version: 5.66.0
Qt Version: 5.13.1
Kernel Version: 5.4.10-1-default
OS Type: 64-bit

ADDITIONAL INFORMATION
After I made this screenshot, I've executed `plasmashell --replace` and widgets were moved to their right places (green frame).

Please pay attention that right border of the yellow frame is about 1280px from the left edge of this display. 

My assumption that on some conditions widgets are placed with coordinates bounded to size of the first (DVI-0) display  and then getting moved to correct display but with the same coordinates.