Missing Favorites list on Vault

I use the Vault extensively and have kept list of hundreds of favorites from the albums in the vault.  With the update to 4.2 (we use android and IoS in the house) the favorites list in the library is missing.
Adding a new favorite created a new list with one song - arrgg!!
Where is the favorites list stored?
Can I locate a back-up?
Can you please describe any changes to the favorites file that were implemented since May.