I've had Spotify on my Samsung Galaxy Note 4 for 2 years without issue. However in the last month my offline music keeps on disappearing and the app defaults to original settings, storing music on the phone rather than my SD card and the download tab is switched to off. This can happen at anytime and when I switch the storage option back to the SD card, the app recognises I am using 5.7GB of storage but the data i.e music is not available. So i have to redownload the playlist and start again. Its happened that many times its driving me insane. I've deleted my cache and data, removed the app and re-installed it, I've searched the forums and online help but there doesnt seem to be anything to remedy the problem. I only have spotify on one device, there are 600 songs in the playlist and there is tons of room on my SD card

Is there anything else that could be causing this to happen?