Welcome to the forum @mortenchristensen
This (according to Google search) is a very rare issue, so there’s not much known about it, but maybe
So I guess I guessed right in that case. Probably best to save as much as possible, e.g. local database which should be easy, and maybe even destination files if it’s possible and backup is critically important although I’m not really super worried about accidental damage to destination. There’s just no guarantee.
So what are orphan files? and how to solve their existence issue? was an earlier round of guess and fix:
and this should not be able to harm destination files, so no need to worry about that. To get back to prior database problem, just put back the copy of the database you saved, and you can try something else…