You probably had some of these movies matched to an older/different metadata agent.
Now, if you change the folder of your library and perform a library scan, all those movies get recoghnized anew and are matched with the current default agent.
The only two possible options known to me are:
- on the old server, change the library’s metadata agent to “Plex Movie” and perform “Refresh all metadata” for the whole library. Only after this is finished, transfer the library to the new machine.
- transfer the whole plex data folder, then edit the database file and change the folder path reference of every media item to the new location: [HowTo] Plex database modification - Moving media the right/wrong way - #10 by jelwell
