[iOS] Can't play individual items on synced playlist, only whole playlist

I synced my entire music library to the iOS Plex app, which includes one playlist of favorite songs.

When viewing the on-device music library, I can play that playlist in order, or shuffle play the entire playlist. But if I try to play an individual song by tapping on it while viewing the playlist, nothing happens (other than the tapped song highlights briefly).

Any ideas?!

iOS app version is 4.10. Server version is 1.5.5.3634 on a Synology NAS.

Thanks!

I made a short video of this to show it better:

https://stevenf.com/downloads/plex-playlist-bug.mp4

As you can see, tapping on any song in the playlist has no effect, except for a brief highlight. Tapping on the Play button for the entire playlist works, but not individual songs.

What could be going on?