Sorry, I don't understand. What is gone? And what do you mean with songs missed? Are they marked as missing after restoring a backup? Did you restore a version 2 backup? That does not work on MacOS because it can not import songs from iTunes. You need to migrate to version 3 on iOS, then create a full backp in version 3 on iOS and you can restore that on MacOS.
But I will add an error message into the next MacOS version when trying to restore a version 2 backup. I forgot about that in version 3.3.0.