I am running suse with a dual monitor setup. When I woke up this morning and turned my screens back on and logged in my primary monitor and secondary monitor roles had changed, with my menu/taskbar now residing on the non-primary desktop. Going into system-settings->display and monitor->display configuration I confirmed that the primary was still checked on the correct monitor and that the displays were identifying themselves correctly. When I set primary to the screen I didnt want to be primary my menus/taskbars/etc… went to the correct screen (but now the primary flag was marked on the wrong screen). I rebooted thinking some update may have caused something, but same issue with the primary flag after reboot. I have left primary checked on my non-primary monitor for now and its working as expected (though I havent tested launching too many things at this time). Wanted to get this post out to see if anyone else is seeing this problem, I dont think switching the checkbox on which is primary should have too much of an impact but seems odd that the behavior, at least for me, with that checkbox changed.
It is a long story, a bit difficult to read because of the complete lack of a structure. As far as I understand it, you are using a desktop environment, but you failed to explain which one.
Please take into account that none of us can read minds. 
Sorry wrote this before I had coffee and was dealing with an issue at work too.
Im running Tumbleweed with KDE in a dual monitor setup. In the display configuration I have a single monitor set to primary. Coming back to computer after I woke up I found my menu/widgets from the primary monitor switched to the non primary.
https://i.imgur.com/yHO9f8s.png
In the screenshot you can see that the left screen has “Primary” unchecked but is functioning as the primary with the menus and everything else. Last night when I went to bed everything was setup on the primary screen (left screen had primary checked on it), with some monitoring widgets on the desktop of the non-primary (right screen). When I woke up the position of everything switched. When I checked the primary on the right screen it essentially made my left screen act like it was “primary” again and reset the widgets that way. When I restarted the computer with the left selected as primary again everything stayed on the wrong screen, so in the screenshot above the primary is unselected to put my panels/widgets in the correct locations by default.
I did not drag my panels to swap screens, it simply happened. The primary setting appears to decide where they go and has been swapped from what it was yesterday.
Hopefully that clarifies things a bit.
Every now and then configuration files get corrupted and systemsettings5 stops working: https://forums.opensuse.org/showthread.php/573380-function-keys-doesn-t-works?p=3150218#post3150218. An easy fix is logging out from KDE, moving the offending files in ./.local/share/kscreen/ and logging in again.
karl@erlangen:~> find ./.local/share/kscreen
./.local/share/kscreen
./.local/share/kscreen/control
./.local/share/kscreen/control/configs
./.local/share/kscreen/control/configs/754ceb37bada586d5e0ba58a4a1f6fea
./.local/share/kscreen/control/configs/91c6bc4fe8d2571b908460aaf8259a89
./.local/share/kscreen/control/configs/9c89d956f72adaf7e4f11170aef9723e
./.local/share/kscreen/control/configs/eea4e4f4bea20baa1322703081fd2332
./.local/share/kscreen/outputs
./.local/share/kscreen/outputs/09d165d6c0f20db8b7455c57415ae3c6
./.local/share/kscreen/outputs/84a7db9688aef0e80b5700f2f8f070e5
./.local/share/kscreen/outputs/908532c826b5364e32135c6fec4645ea
./.local/share/kscreen/outputs/b9fa02524644b2efd4a3ef1e00bd0d3b
./.local/share/kscreen/outputs/c21f969b5f03d33d43e04f8f136e7682
./.local/share/kscreen/754ceb37bada586d5e0ba58a4a1f6fea
./.local/share/kscreen/84e3f5c77f0b16198793aff8d16ab54d
./.local/share/kscreen/91c6bc4fe8d2571b908460aaf8259a89
./.local/share/kscreen/9c89d956f72adaf7e4f11170aef9723e
./.local/share/kscreen/c21f969b5f03d33d43e04f8f136e7682
./.local/share/kscreen/e271dce28c6db3c6c63c8f5660c6b99f
./.local/share/kscreen/eea4e4f4bea20baa1322703081fd2332
./.local/share/kscreen/kscreen.log
karl@erlangen:~>
When logging in again pristine files are created:
karl@erlangen:~> find ./.local/share/kscreen -type f
./.local/share/kscreen/outputs/84a7db9688aef0e80b5700f2f8f070e5
./.local/share/kscreen/9c89d956f72adaf7e4f11170aef9723e
karl@erlangen:~>
Thanks will try that if it happens again. Didnt happen on my old build which ran quite a few years, fairly new on Tumbleweed so it was an oddity. Will mark this down if it happens again.
I see this is LEAP when the primary monitor is off during login, KDE will then set the other monitor as primary.
Usually setting it back in systemsettings -> display is enough.
Did you try the Save display’s properties in display configuration in systemsettings5?
There are two options one might work plus disabling probably the “kscreen2”.