New error message after recent PLEX update blocking all most movie playbacks “Conversion failed. Transcorder exited”

Plex Media Server NAS & Devices
,
16
  • “They do something very strange”

Synology, for whatever reason, has reserved the right to control permissions of the default video share as they deem appropriate.

The primary way it manifests is by removing share access OR direct modification of the ACL on the directories in favor of Video Station.

Did you receive a DSM update recently? If so, then the re-application of Synology-default permissions cannot be overlooked.

User plex is no longer an administrator on the device (as of PMS 1.15.4.994) and cannot override those restrictions.

Ref: Plex Media Server security changes for Synology users

Regarding the error in your log and this file becoming “Not Found”:

/volume1/video/Com MOVIES/The Anonymous People.mp4"
  1. The file has truly been deleted ?
  2. It’s a symbolic link or under a mount point which resolves to ‘nothingness’ now.
  3. The permisions of /volume1/video no longer let user plex read it. (most common)