iTunes playlists sync but empty

Every since I signed up for Apple Music, my iTunes on my phone has been a disaster. Artwork disappearing, ratings getting applied to albums instead of songs, etc. At first I found I could fix things up by deleting all my music and resyncing, but now nothing is working for one of my playlists.

The playlist in question is a smart playlist with three criteria. On my Mac, it has 15 songs in it. On my phone, it's empty. Nothing worked to get the songs over there. So I created a new version of the playlist with a new name and the same criteria. Same result: 15 songs on the Mac, empty on the phone.

I'm not an iTunes hater, but it hasn't worked right for me, consistently, since the launch of iPhone 6.