There is a problem with DSM 7.1.1 Update 7 affecting multiple non-Synology applications.
Synology has said a fix will be available by the end of February.
The problem affects only DSM 7.1.1 Update 7. If supported by your NAS, updating to DSM 7.2 or 7.2.2 resolves the problem.
If staying on DSM 7.1.1 Update 7:
To stop/start Plex Media Server, see FAQ 35: Start/Stop Plex using Task Scheduler.
To update Plex Media Server, you do not have to stop or uninstall the current version. You can install the newer version via Manual Install.
If you need to uninstall Plex Media Server, you can uninstall via synopkg uninstall PlexMediaServer.
You can also SSH into the NAS and use the Linux CLI: sudo synopkg <option> <package>.
