Not all tracks in my PLEX music library appear when using the SONOS controller. It is like the SONOS app is stuck on an earlier (un-updated) version of library. I have tried removing and re-adding PLEX with no result. Some of the missing tracks have been initially drawn from TIDAL, but this does not appear to be a consistent explanation.
The connection with the PLEX server can also be a very random affair, but that’s another story.