My co-op is bugged! Please help 343i!

My co-op is bugged/glitches or something. For some reason half way through a mission my brother friend and I are playing two different campaigns on the same level yet we can move in each others game however the games are not synced, so when he’s in a different part of the mission his character on my screen is playing as if he is in a different part of the mission yet if he is in a battle on his screen he looks as if he is battling no one but air and most of the time ends up falling off of the map because he can’t see what I see. I know this sounds weird but that seems to be the case. Help would be appreciated.

You don’t state in what game you are experiencing this in. But i’d say Halo 2, since it have been a well known problem since release date, and apparently haven’t been fixed yet.
what level does the problem occour?