like tungsten mentioned it could be the wide gale hook on a she if that is the rig you are using, second it could be timing aswell being a little to late, another could be the distance between flies ifthey are too close u will foul more Iime 16" or so between flies and another option could be strikin on super subtle takes were u are just lining the fish and not getting takes but it is rubbing along side th because they are stacked on a seam or dropoff you are fishing... hope thet helps!