Mac mini M1 Plex server fails to add video files that Synology NAS Plex server did

If the media is still on the Synology, also review the thread linked below.

There is a problem with SMB in the current version of MacOS. If you’ve many (1000+) movies in the library, Plex may not find all of them.

As a workaround, you can modify a SMB config file on the Mac or use NFS instead.