My guess is you were killing members of both teams, zeroing out any progress.Thanks for responding @Kyronix.
I was casting meteor storm into bad guys, running back to mob, invis, and pick off individual bad guys while the myrmidex chewed them. Is there a timer? Because both times I went over the two hour Mark? I know in each case the banners said I had killed 17 of 20 wave 3 of brits. This is what led me to think it is broken.