My Plex server crashes immediately on my Synology DS418 DSM 7.1.1

Bingo !

That tells me a lot.

  1. Question: Who’s been playing in the Plex shared folder ?
    – Do you have media in there?

  2. Look at your logs. PMS can’t write to its own files.

  1. Notice the date/time stamp. Everything should have updated.

Does this help track down the culprit?

Lastly, I can get you back on track.

Follow the instructions as written.

Share the results you get from your email when done if any errors