I use Samsung Music on my S9 to maintain a playlist called 'Podcasts for Watch' which I have autosynced to my Galaxy 42mm. The first issue is that the Music app doesnt see my music or podcasts in their native folders and I have to copy them to one called 'Music' for the App to see them.
When I add podcasts, or music, to the Playlist in Music, nothing happens on my watch, even though Auto Sync is turned on for that Playlist. I have to force the playlist to sync by turning Auto Sync off in the App and then turning it on again. Not a massive inconvenience, but I cant believe the App and sync process was designed that way?