At work I've had issues with the Start Bar not showing any/most programs and centering the one program that does show up (even though I have it left aligned). Then when I mouse over it, it'll try to move to where it should be causing it to jump around and be unclickable.
I've also had the file explorer just stop working entirely.
This is on a pretty powerful dev laptop, so it's not lack of resources.
That being said I've never heard of anyone else having that issue so it seems rare.
I don't believe that is a KDE specific issue. I've seen it in most DE's
It's more of a mount/file system limitation. For whatever reason you have to explicitly tell the file system that if it can't connect to something, to timeout.
Add a timeout to your mount rule and if it ends up being unavailable it'll just timeout instead of freezing your file browser.