online CO OP campaign intense lag

Halo 3 campaign suffers from awful lag when I play with friends and I’ve never experienced this before up until recently

We each tried hosting the game and the results are always the same; I.e the hosts game is buttery smooth with little to no lag but everyone else is lagging and freezing up.

The issue seems to go away slightly after playing some missions for a bit or when it’s later in the night.

Online multiplayer matches and private games are never like this at all.