It could be all the tinkering and manual fixing/deleting before got this messed up.
If you don’t yet have much of a watch history you could simply create a new library, point that to F:\Media\Series\ and go ahead from there.
If you don’t want to nuke things like this you could alternatively remove the Arrow folder, re-scan the library, empty the library trash inside Plex, return the folder in place and re-scan the library a final time… this should bring the show back (Plex Dance).
