sometimes the archers will start bobbing back and forth without shooting, they kind of walk a few steps in each direction really quick, takes them several seconds before they get back to shooting (sometimes while surrounded by enemies, gets them killed pretty quick).
Perhaps its because they cant decide which enemy to attack? If its that, you could try adding a function where if theres an enemy in range and theyre not moving to defend tower, they dont stop shooting (or not, im not a game dev so theres probably a better solution)