Library scanning seems to have stopped working on my Synology 918+

[Thumpermat]

My guess is that you haven’t changed the security access for the user plex on your synology. This happened since the last release. See the following article.

Plex Media Server security changes for Synology users

Additional benefit to using Read Only media shares. By leaving your main media library as Read Only, only you can change them. Plex cannot touch them in any way. This only seems problematic at first should you want to optimize the media or have a place to store temporary DVR recordings. Since Plex allows multiple folders to be included in a library section, the solution is quite simple. Leave your main media library as Read Only a. Nothing can delete your media except you b. Even if …

Hope it helps.