DS920+ running 7.0.1-42218 and Plex 4.69.1
I’ve been encountering this for a week or so as well. I had attributed it to the Youtube Agent or ASS being flakey, but I’ve noticed the issue crop up in Libraries managed by Plex TV Series in addition to the more custom libraries. As others have mentioned a reboot will resolve the issue for a time. I’ve been keeping an eye on the logs and nothing is jumping out at me thus far. I have noticed that when the bug is occurring any attempt to have Plex rescan the Library files will just do nothing as far as the logs are concerned.
I’m wondering if it’s possible that recent Synology changes have tweaked something around the max folders that Plex can manage mentioned in the Syn FAQs and now Plex instances above a given size are now encountering race conditions based on file load and cache once the service restarts. It may be worth noting that my media dirs are a good bit smaller than what is listed in that example, but I’ve implemented the proposed fix and will see if that has any useful effect.
This said, I’ve also seen some odd behavior with services accessing directories/files with Syn Photos recently so the problem may be larger in scope than Plex. I know in that case I had to actually log into DSM proper and go poke around in the File Explorer to kick things into gear; though that hasn’t worked as a fix in Plex’s case.