I keep having a problem where my offline tracks are being removed from my device. I like to keep my entire library (two thousand something songs) stored on my device by simply checking the offline option for all songs, but every few weeks, the option randomly gets unchecked. Usually, it's just the offline option on the whole songs "playlist," but recently it has also unchecked the option for other actual playlists I have saved offline. I use my offline tracks every day so it is frustrating when I end up somewhere without service and can't even stream the songs. This has happened probably 5 times but I haven't noticed a pattern.

I only have two offline devices attached to my account (phone and laptop), and the laptop doesn't have any offline tracks saved. The phone is a Nexus 6P running Android 6.0.1.

Any help would be appreciated