Garmin Express Mac has lost the ability to sync music.

Express version 7.23.0.0, Mac OS 15.0, FR265 version 20,29

Symptom: Express loses comms with the the 265 after 'music' tab is pressed (Please plug in your device error). It is not a bad connection as other portions/syncing function normally. Everything works as it should on a PC. Multiple cables have been tried, as has a factory reset on the watch. 

Express has been uninstalled and reinstalled. 

I have run out of ideas.