I have two plex servers with a mirrored library.
Server 1 (skinny) is version 1.24.0.4930 running on gentoo linux.
Server 2 (blackbox) is version 1.21.0.3744 running on a synology nas. (the latest version available)
blackbox is missing some of the files that skinny detects. The files have identical md5sums and permissions. I have restarted and re-scanned blackbox. I can’t find commonalities between the missing files - they are a mix of mp4 and mkv.
Any suggestions on how to get blackbox to see the missing files?
What Synology model?
What version of DSM?
Missing files generally comes down to permissions or file naming & organization.
Can you provide the naming & organization for one or two of the missing files?
A directory listing, screenshot, etc. Show the full name & path, if possible.
Example using File Manager on my Synology:

Here’s skinny
0 skinny pms/mpt % ll Halloween\ *
'Halloween (1978) {imdb-tt0077651}':
total 1569524K
drwxr-xr-x 2 brundage brundage 4096 Nov 6 18:24 ./
drwxrwx--x 149 plex brundage 12288 Nov 13 12:55 ../
-rw-r--r-- 1 brundage brundage 1607170013 Oct 29 21:35 'Halloween (1978) {imdb-tt0077651} 2021-10-29_19-04-43.mkv'
'Halloween II (1981) {imdb-tt0082495}':
total 2025492K
drwxr-xr-x 2 brundage brundage 4096 Nov 6 18:24 ./
drwxrwx--x 149 plex brundage 12288 Nov 13 12:55 ../
-rw-r--r-- 1 brundage brundage 2074083328 Oct 30 00:59 'Halloween II (1981) {imdb-tt0082495} 2021-10-29_21-43-12.mkv'
And blackbox: