Most of my music disappeared from my iPhone on a trip to Europe

On a recent trip to England and France, much of the music in iTunes on my iPhone 11 Pro appeared grayed out. When I tried to play a song, I would get a warning saying, "This song is not currently available in your country or region." All of my music has been downloaded onto the phone for years. On my return to California, all of these songs, plus many more, continue to show this warning when I try to play them. I've taken this phone to Europe before without any issue. What's going on?