Thank you for using Apple Support Communities. It's my understanding your Apple Music Library is missing after it was previously working without issue. My music is often the most valuable content on all of my devices, I can surely understand your concern. I'm happy to help. Please follow the steps below:
Get help with iCloud Music LibraryIf you can’t see iCloud Music Library on your iPhone, iPad, or iPod touch
First, restart your iOS device.
If you still can't see it after the restart:
- Turn off iCloud Music Library and then turn it back on.
- Sign out of the iTunes Store and then sign back in.
Have a wonderful day!