Disease is always a consideration when trying to figure out why chicks die. You should read up on the manchurian lethal gene and see if apply to your situation. The next setting of eggs, I'd mark your eggs separate from the ones you buy to make sure its your dying. If you have already done that, remove one male and try a different male. You'll need to change cages up though to prevent the hens from attacking him. Ive had to do some of these things for my own flocks when I had an undiagnosed problem with dying chicks. I ended up having what I think was MG.
