Can't play system link anymore

So my girlfriend and I own all the same DLC. We’ve played the game hundreds of times together. All of a sudden, we can’t. When one of us tries to join the other, it says that the host has different version of the game or different compatibility pack.

So I deleted the compatibility packs on both, deleted the title update on both, cleared cache on both. Re-updated on both, re-downloaded compatibility pack on both… And still we can’t do system link.

So I deleted ALL of the DLC and the compatibility pack, and the update, on both. Reinstalled and re-updated EVERYTHING on both and STILL we get the error message when we try to do system link…

I contacted xbox support first. They gave me the usual support. Clear my cache. Delete my profiles. Redownload patches and DLC. In other words, all the stuff I’ve already tried. And then they told me to contact 2K support. Which I did. A week ago and I haven’t heard back…

So… What now?

Oh, and off and on, our DLC characters (Kreig and Gaige) show up as !Unavailable!