It’s a bug which affects only one user and not the whole graphical desktop, but only the “desktop” in a narrow sense.
A workaround can be to rename the .config folder (to something like .config.old) so that you can get anew your whole graphical desktop and then maybe you could copy (prudently) one by one your config files (from .config.old to the new .config folder).
In KDE Linux it could happen some issues with windows:
- rules not memorized: to fix it check if configurations files (tipically in ./config/ kwinrc and kwinrulesrc) have the right permissions (avoid: non access).
- new window below others already active: such as Clementine’s window, called from system tray, going below other windows; to fix this you have to set Focus stealing prevention in Window Behavior (the first tab of Window management in System settings) to none, as you can see in the image