KDE does have focus stealing prevention, Have you messed with that at all? https://docs.kde.org/stable5/en/kwin/kcontrol/windowbehaviour/index.html#focus-focusstealing The only thing I can think of is maybe some notification steals the focus and doesnt give it back to the window.

This happens on my Pixel as well. I forget which launcher I use but I keep the icon on my homescreen so I can just hold it to get the app info and force stop it.

Do they support port forwarding?