You guys are hosting the game on your consoles...effectively your console becomes a server in the client-server communication cycle. Make sure you guys are able to communicate effectively with each other. May even need to bring your ISP's Tier3 team on board to watch your data as you play. The players broadcast data to each other via UDP. ALL of you need to have an inbound path open for receiving those streams. That goes for everyone in the instance. Whoever is not receiving those broadcasts must wait for the other players to synch with Bungie in the background first, and then have their console synch in the background to get those updates. It can cause things to get grossly out of synch. Too much delay or dropped packets can cause you to loose the session altogether, getting you booted. One of the easier ways to open the UDP path is via UPnP. Enable it in your router, check your console's network settings and enable it there if you have the option (may need to manually configure it for the option), then run the connection test to make sure it registers properly with the protocol.