After plasmashell restart, the panels are placed on the incorrect physical monitor in a xrandr multi-monitor setup. Reproducible: Always Steps to Reproduce: 0. Your primary laptop screen holds the panels 1. Connect a bigger, second monitor to your primary (laptop) screen 1a. Issue xrandr command (this sounds like a bug too) 1b. Open system settings and enable the screen 2. Place the new screen to the left of the old screen (share an edge and the top corners) 3. Restart plasmashell (e.g. due to notorious high CPU usage reported elsewhere) using kbuildsycoca5 && kquitapp5 plasmashell && kstart5 plasmashell Actual Results: Panels appear on the external screen and disappear when it's disconnected or disabled. Expected Results: Panels appear on the same screen where they were. Intel graphics, HDMI output, LVDS builtin panel. Workaround: with the external screen connected, open panel properties, and drag them back to where they belong. Be careful not to stop in the dead zone below the smaller screen or the panel will disappear again until next restart.
This should be fixed with several changes to the multi-screen stack in Plasma 5.8. In case you are still able to reproduce with Plasma 5.8 please reopen.