bad eggs

I have a pair of Racing pigeons up until this year had no problems they are healthy and I see them mate and then two eggs they stay on them good but the eggs don,t hatch would there be any other thing other then the Cock went Sterile he is 10 years old but healthy.

Can anyone help me understand why this happened? In our first round of breeding three pair each laid 2 eggs which is normal. All six eggs hatched and that the 6 YB we are training now. Then come round two same three pair each laid two eggs. The first pair hatched one egg second one infertile...