A couple of weeks ago my iPhone stopped displaying my complete library of music. Normally I can just stream anything from my music library whenever I like, but when my AC/DC albums went missing I was not happy.
After some hunting around I discovered a delightful setting that makes no sense in iOS 9. I don’t know why you would switch it off but there it was.
Make sure “iCloud Music Library” is switched on. When I did this it asked if I wanted to merge or replace the local library. I just replaced because I know all my music is in the cloud. After a couple of minutes my music library was repopulated with all my aural pleasure. Happy days!