iTunes .xml file missing. How do I generate a new one?

I'm running Supersync to sync my iTunes libraries across my computers. Since upgrading to iTunes 12.2.1.16, Supersync hasn't been able to find the .xml file it uses to link the multiple libraries on one of my computers. Upon investigating, I discovered the .xml is in fact gone. I can't find it anywhere. iTunes functions fine, but my old playlists are all gone (though I honestly don't really care about that). I have found all kinds of articles and forums about using the .xml to restore the .idl file, but I can't find any way to restore the .xml outside of creating a whole new library, which I really don't want to do. I have no idea why the .xml is gone or where it went.

This all started while I was on windows 8.1, but I have since upgraded 2 of these machines to windows 10. No change. One machine is fine, the other one still is missing the .xml.

Someone, please tell me, how to get that .xml back?!

Thank you.