What Perry said about drones. The near formed ready to emerge have large drone eyes Could be a ground hog type of scenario. with the cool weather the bees though winters not over we don't need to be feeding these boys yet. Or could be just where they were located on the edge of the cluster.
The only 100% sure way to know is to go in and take a look. Even then it may not be totally obvious. but would tell if it is random through the cluster or from an exposed side. The different between chilled brood, drone culling, and pests, pesticides, and disease.