Sounds like you copied/cloned your original server when doing your original migration. This will leave both machines with the same identifiers. Stop that server and try manually deleting those identifiers.
Preferably create a backup of the actual file in case you get things mixed up.
~/Library/Preferences/com.plexapp.plexmediaserver.plist
I’m not 100% sure if you need to delete all entries but those should be the ones in question:
AnonymousMachineIdentifierMachineIdentifierProcessedMachineIdentifier
To delete each property, best use the following command in your Mac’s terminal:
defaults delete com.plexapp.plexmediaserver <key>
Where <key> is one of the 3 property keys listed above.
