I have a fully updated iPhone 6s, and have tried un/re-installing the app, and resetting the other Spotify device authentication thing they recommended. But still, when my battery dies, I am logged out of the app and I lose about 4000 songs. 

I have cancelled Premium and am imminently going to start using Apple Music, because Spotify just does not work. I realllllllllly do not want to give Apple any more money and Spotify was perfect before this. 

I'm sure I am not the only customer to use Spotify 85% offline and 15% online, so offline playlists are essential. 

Has anyone else experienced this bug? It is a make or break issue for me. Please don't make me turn to the dark side.