For the most part YouTube music has been something really awesome. Not sure why it's happening now all of the sudden, but once in a while I'll login to the app and hit up my downloads to play my daily dose offline. Very recently a bunch of my downloaded music will appear normal but if i try to play a song, the app will say cannot play song temporarily. Then if i check all other folders, every other song will do the same thing. It forces me to delete all my downloaded music and start over.