I find that if you see a weird split like that or a rainbow, look to the group that played right before them. Usually a bad performance. The next group you have some judges relieved to hear better and may over reward, and some that will still be grumbling about the problems with the previous group and the second those show up in the least they will hit it hard. These are of course not conscious decisions, but just the way different judges might react. Yes, you are supposed to independently judge the performance of the group in front of you, but we're human.