Ok, looks like I'm talking to myself in here, but whatev.... sometimes thinking out loud helpsl I'm now getting convinced the problem is in the widget or lock screen. I've disabled both, cleared the app cache, wiped out all the music and playlists on my phone, and then re-loaded them from MediaMonkey. Guess what... It's working again! The .m3u playlists are showing up again with all their songs, and I can play them directly! Yay! We'll see how long it lasts, and maybe someday I'll be brave enough to try the widget or lock screen again.