On the watch you can select different "Music Providers" under settings->Music. "My Music" lets you play tracks loaded in the watch's internal storage from the PC through Garmin Express. There are various other providers available for different sources.
Normally with My Music selected I can play all tracks or browse by artist, album etc. However if I switch to a different provider, such as Podcasts or Amazon, then switch back to My Music, everything is gone. It says "no tracks found" when I try to browse. Turning the watch off and on again makes the tracks reappear.
I'm curious if anyone else has encountered this or knows a solution. The main issue for me is I sometimes want to switch between podcasts and internal music, and I don't want to turn off the watch during an activity.