I can only say: it happens, although it shouldn’t; or at least I already saw this occurring in the forum and on the internet.
For this:
Try to give a look here:
In general, you could start searching on the internet where KDE stores those configurations and backup the relevant files.
Only as an example, at a quick search, I found this (it is old, to be checked if everything is still applicable):
https://forum.kde.org/viewtopic.php?t=151477