I have somehow similar problem, so maybe instead creating another thread I will hook up on this one.
So I use latest (5.04?) version of 4.4.2 AOSP by slv96 and Google Play Music. I've discovered that everyday my Music Libary is resetting, so I have my playlists but they're empty, and 'Liked' playlist is gone aswell. I'm wondering what's causing this to happen.