Created a new library and added an empty folder, then created a sub folder which I added correctly titled music video video files to, then they were scanned into Plex fine but other mystery folders appear.
I have checked my NAS share and there are no movies in this share/folders by this title. They look like movie titles.
I can replicate this issue by crating a new library with different music video files and same issue occurs.
Would you mind double-checking / sharing the Add Folder screen? Is it correctly pointed only at the folder in question or are there any ghost references?
Have you checked the folder in question using admin permissions on your NAS (e.g. the folders exist but are not visible to the currently used NAS account)?
Can you double-check the file system on the Debian machine?
Are there possibly any collisions on how the Debian host is mounting the NAS drive, that might result in more folders showing up in Plex?
I think you’d agree that it’s reasonable to assume Plex server is not able to navigate beyond the top-level directory set in the library path - by design.
If you can validate my assumption, I think it’s then fair to say that any potential issue arising from directory traversal is unlikely.
I can confirm top down, this is the full path where only the last subdirectory only contains video files (mp4)
\NAS1\multimedia_ext1\Music Videos\Music Videos - Playlists\90s video\50 Cent - In Da Club.mp4
Also, I can confirm there is no customization such as symbolic links or any other additional complexities or containing video files which resemble the folders added by Plex server.
I have intentionally created 4 libraries to keep the videos easier to navigate due to the lack of Music video support in Plex, and I am seeing this issue in each library.
Music Videos - Playlists
Music Videos - Artists
Music Videos - Genres
Music Videos - Years
Last point, I did have the music videos added a couple years back with the old versions of Plex agents (also using Personal Media agent) and never had this issue.
Looks like after the last scan of the mentioned video folders, the false movie folders changd. From what I can see there are 2 movie folders now with titles of the most recent movies added to the Plex Movies library.