They are programmed to attack and briefly run the opposite way between each attempt. I am sure they are all just doing that in unison.

Small details like that can make a mob feel a lot smarter and group-oriented than they actually are.

Like I think if archers were taught to stand their ground when they lost sight or at least stay a certain distance from your last known location rather than running all the way, that would be a dramatic improvement. They are quite a hassle in spaces like dungeons until you realise you can bait them to run into melee range by hiding behind any old cover.