Hi David & Apple_iOS
Some users are able & unable to download songs offline is because some of Apple Services are down. I was also wondering why the same thing was happening to me, started happening since 7:50AM MDT here in Canada.
Here's what's currently down
App Store
Apple Music
Apple TV
iBook Store
iTunes in The Cloud
iTunes Match
iTunes Store
iTunes U
Mac App Store
OS X Software Update
& Volume Purchase Program