Thanks for reaching out M1872,
It sounds like you recently had your music downloaded from Apple Music for offline play disappear. We can help.
There are a few reasons you might have your offline music removed from your device:
- If you sign out of your Apple ID for any length of time the subscription can't be verified and all music is removed until you sign in with an Apple ID with an Apple Music subscription and download them again.
- If your Apple Music subscription is cancelled.
- If your Apple Music subscription is unpaid.
- If your iPhone is low on available storage it will delete music files to free up space to make sure your iPhone continues working.
If one of those seems like a possibility, once you address the issue you should be able to redownload your music and continue as normal.
If none of those seem like a possibility, you can Contact Apple for support and service to report the issue.
Hope that helps.
Take care.