Have you flipped the "Download" switch for that playlist in your Android app? The playlist shows as empty because you haven't downloaded/synced the songs from your computer to your Android and you have disabled "Show unplayable songs" in your Android app.
If you've tried all these 'solutions' and still can't access/play your local files despite physically seeing them in-app:
1. turn on your iPhone hotspot and link your computer to it.
2. search your computer files for the music you want (put it into a single file if you have more than a single album you want synched up)
3. copy this album (which is probably in the iTunes file within your music folder) and paste it OUTSIDE of the iTunes file in the general 'Music' program file
The songs should start to synch immediately. They at least did for me, after I spent an hour fumbling around trying and failing with all the aformentioned solutions in this thread. Hope this works for you, too! 🙂