Were the cochins fertile before or are they not laying? Could it be the weather? My orp's fertility takes a nosedive in the winter. The roosters are always less active in summer heat as well. I think they're just big & lazy. I never have those issues with seramas.We lost a few toes from a raccoon that preferred toes to spilled chicken feed. But I did put a bullet in that one. So I've got a wee flock of Seramas, a reverse trio of Call ducks, a quad of Lemon Blue Bantam Cochins that aren't producing fertile eggs, and nine Bantam Orpingtons (Chocolate, Mauve, and Blue?). Those were all in super-secure pens that she's never messed with. I'm a bit disappointed with the Orps. Ended up with six cockerels and three pullets. All but one cockerel has leakage and some of them are so leaky they have more incorrect feathers than correct ones. And one of the pullets is leaky too.
Sorry about the leakage in the bantam orps. The male/female ratio sounds about as good as what @homeschoolin momma gets. She defies the odds with her % of male hatches. At least orp cockerels can make a meal. Not so much with the bantams.