Strange. It seems like a bug to me but in not involved with KDE. I would still reach out to them. Perhaps they know more at the KDE forum of how it’s supposed to work.
Hmm, this all seems to be a work around for another issue. My computer remember the position and settings of all men screens when replugging them. It seems your system doesn’t remember the display configuration.
Perhaps reach out with an issue to KDE on their issue tracker?