Those blazes are busy shooting some target on the hill. They become unresponsive to any move orders away from the cliff. Replay ID = #9758988 Bug happens at around 30 minutes.
Okay that should help. I do feel though that there is a need to adress this. The blazes seem to be magnetically attracted to the target they are shooting. I could see that some broke free and just bounced back and forth on flat terrain between their move target and their shooting target. This seems to me like it should not happen in the first place.