Sounds like my problem. I have a significant amount of offline tracks and playlists that are no longer playable in my iPhone 5s. I don't play them on any other device or computer. What gives? I even tried searching for one of the song to see if it'll play while in the search field (instead of playing through my playlist) and it still doesn't work. I've been a prime member for a few years now and this has never happened before. Hoping someone can help.