Also with flatpak install --reinstall package_name?
Another thing that could be tried is the use of flatpak remote-modify with --update-metadata. Never used this command, but why not? See Flatpak Command Reference - Flatpak documentation .
Contrary to what I said before, I think I had already had this checkback error (but a long time ago), and waiting did the trick. How long? I don’t know. Sorry, I don’t have any other possible solution.