Amazon music "access expired"

I opened Amazon Music to play a downloaded album and was startled to see a message that said "access to downloaded Amazon music has expired. Please connect to the Internet to refresh." I've never seen that message, and I have a lot of downloaded music; much of it, like this album, was a free MP3 with purchase of a CD. I haven't checked all of my albums to see if any others have that message, although I did open a couple and didn't get that message. And the phone is connected. I don't have an Amazon Music subscription, just the music app; I'm also a Prime member. What's this about? I will try to find an answer on Amazon's website, but the last time I looked for some info there it was hopeless.