SUMMARY
On my system, where it may be relevant that the screen is 3840x2160 with a scale factor of 200%, and a second screen, which is 1920x1080, scaled to 100%, on Wayland, experiences an issue when accidentally deleting and then undoing deletion of the bottom panel.

STEPS TO REPRODUCE
1. Enter edit mode on the default bottom panel
2. Right click the panel, remove it.
3. Click the undo button on the balloon that pops up.

OBSERVED RESULT
Panel restores itself vertically centered on the screen, just above the center. Possibly with some of its widgets rearranged. Panel cannot be moved to the bottom of the screen, and the editor thinks it is already on the bottom of the screen.

EXPECTED RESULT
Panel should restore to the bottom of the screen. Panel should restore its original arrangement of widgets.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux, KDE Plasma 5.27.5
(available in About System)
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9

ADDITIONAL INFORMATION
This may or may not be related to screen scale factor, or Wayland session.