Playlist changed from being available offline by itself. Bug or something else?

[oats573952]

I logged into my account via a freshly installed iPhone app on a freshly restored iPhone running iOS 9.3.2 (the latest). After I logged in, I ensured that all my playlists would be able to be listened to in offline mode by sliding the bar to green next to "Download" for all of them.

While I waited for the process to finish while periodically checking the progress (it was about halfway done), I had noticed that one of the playlists had been changed from being able to be listened to offline to regular online listening mode (so the little button next to "Download" had slid from right [showing green space] back to the original left [showing black space]).

I definitely didn't do this myself, the phone had just been sitting on my table, I didn't accidentally slide the button while checking on the progress and no one else had accessed the phone while the offline conversion was going on.

What could have caused it to spontaneously change from offline to online mode?

Has anyone experienced something like this before as well?