iTunes music Library empty
I've had success in the past using iExplorer to view files in an iOS file system and iTunes backups. I will add as a caveat that these were native iOS devices and not jailbroken, so your mileage may vary.

High level: install iExplorer on your computer, run it, connect the affected device, unlock it as required, and see what files it finds using the various menus on the left column.