If you login and see any of the music from My Library missing...
i.e. Favorites, offline, playlists, etc..
It's likely because you accidentally logged in a different way than usual - maybe accidentally using a different email address.
1. Log out
2. Login using your email and password - or follow this link.
3. If you don't remember your password, select 'Forgot your Password'. This way, you can setup a new password and login using the email associated with your Audiomack account.