Syncing wont continue after I play a song

[Lmac19]

I set the playlists I wanted to be synced as available offline...then later before it was done, I played a song set to be synced, but not yet synced. I discovered that upon playing a song now it will sync when the song is finished, but if I'm not playing music it won't continue to sync. If someone could help it would be much appreciated as I don't want to have to listen to all my music at once to sync it.