That really grinds my gears
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.