When connecting a different display to my system and removing the previous primary display, the panel containing the kickoff is offscreen and not recoverable without changing the LastScreen key in the ~/.config/plasma-org.kde.plasma.desktop-appletsrc back to 0. If the value of LastScreen is 0, this isn't a problem since there will always be a 0 display. However, I like to have my kickoff panel on my non-primary screen so that it is visible with fullscreen video/games, making LastScreen for this panel non-zero. I'm running the latest version of Arch. I am also running the amdgpu kernel video driver FWIW. Since I frequently move my PC around the house between different monitors and TVs, I've noticed this problem. Verifying the actual display with widgets/panel is connected might be a good way to go, or perhaps providing an option to gather all offscreen panels and widgets to a visible display might be good to preserve user preferences.
Possibly related to https://bugs.kde.org/show_bug.cgi?id=380203
Sorry i meant https://bugs.kde.org/show_bug.cgi?id=377588
A lot has changed since this bug was filed. Is it still reproducible for you in Plasma 5.25? We did a lot of multimonitor reliability fixes in that version.
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This bug has been in NEEDSINFO status with no change for at least 30 days. The bug is now closed as RESOLVED > WORKSFORME due to lack of needed information. For more information about our bug triaging procedures please read the wiki located here: https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging Thank you for helping us make KDE software even better for everyone!