ALL of the lag problems, ALL of the bad host problems, EVERYTHING that ANYONE complains about concerning LAG is ALL 100% due to two things.
1) The host is downloading or streaming some crap while playing and it's killing his signal.
2) People who are NOT LOCAL are in the game, either lagging horribly, or they get host and screw everyone in the room with a yellow/red signal
The first can be fixed with proper host migration (I thought they promised it would change host if his signal dropped due to downloading/streaming, they need to get to work on that ASAP) The second can ONLY be fixed by locking the matchmaking the LOCAL ONLY!