This has been covered one way or another in several topics and you should really do your homework - in this case - search before asking.
I cannot say I have experienced anything like you describe.
The issues you describe is likely present because you have neglected to clean your kde and plasma related settings and cache.
You find the settings scattered in ~/.config and ~/.local.
While removing those from ~/.confg and ~/.local requires a granular approach - the .cache can be zapped at any time.
It is - however - recommended to do while logged out and using a TTY.