This has been an adventure... as I first blamed the ISP and have been in touch with them a couple days, then my network and have been testing my hardware, and eventually narrowed it down to this one map called Core Prime Corrida.
It's not an official map, but for some reason the game will go from 0.5 Mbps at the start to using 1.1 Mbps per machine within 10 minutes. This then maxes out my upload speed and bringing the entire internet at our house to a halt.
Any reason it's doing this?
And is there a way I can fix the map so it doesn't?
It is an all metal map, not much bigger than the official big square maps.