I don’t know what happened, but I added another movie today and Plex matched it immediately.
So the short plex dance of
- turn debug logging on
- add a movie or refresh the title matching
- turn debug logging off
worked for me.
But other users may be helped with the dance that PunkleJones described.
Thank you all for your input.
(Plex server on Synology 7.2.2 NAS with Intel chip)