So, I read a forum post that said one of the issues with playing the Halo 2 campaign in co-op was related to it being on an external HDD rather than the internal drive.
I could not hook up with a friend to play the campaign, we were always disconnected.
So, I moved the game over to the internal drive and it worked. We could all the sudden connect for a co-op play through the Halo 2 campaign.
It would still be nice for 343i to fix this issue, I shouldn’t have any issues just because the game is on the external drive.