This problem has infuriated me across 2 different handsets (Samsung Galaxy S3 and Google Nexus 4) to the point now where I will cancel my subscription because it is costing me in data without me realising all of the time. Here's my issue:
I download playlists for offline use over wifi and the download icon appears and goes up to 100% when all of the songs have the green icon next to them and have downloaded onto the device. But then after an hour, day or week later songs will undownload themselves in a sporadic fashion. It doesn't affect a particular song or playlist, just seemingly whatever it feels like.
I have tried:
It irritates me no end because Spotify is a great product but I feel like I'm using a beta release of your app because it never works exactly as it should. I'm inclined to go back to the model of buying and owning my own music because it's downright inconvenient and annoying. I spent all morning redownloading all of my songs before I set off on holiday. This was after a fresh install of the app. Then within minutes of me setting off the songs disappear.