I remember a few years ago going on an international flight. I had Spotify premium and I spent a few hours sorting and downloading playlists and podcasts that I wanted to listen to on an eight hour flight. Tested, retested and everything worked fine.
Got on the plane, fifteen minutes in turn on my device to play some music … NOTHING WORKED … all the downloaded files I had set for offline were unusable. I couldn’t believe it.
My next flights were like yours … just downloada bunch of stuff and play them freely without headaches.