Is the windows side up to date? Most likely culprit would be a db mismatch if one side or the other is on a different version. Similarly, do you by chance have either side running a beta release? If you have plex pass you potentially have access to these
Shameless moment to plug the idea that you could consider migrating to Jellyfin if you can’t solve the issue
This is basically my answer. I would wish my NAS was more full. I already have a pretty (imo) decent homelab with a lot of shit on it but in a “post internet” situation it would get old after a few months or maybe years depending on how fast I watched/read/listened
So tv/movies/music/books/comics and manga. Just all the media