Just a thought...
How long has it been since you added new blood to your flock?
Birds can be bred to family members more closely than other species but after a while problems can arise. I've read one of the earliest signs can be viability and fertility problems.
Because of this many breeders produce 2 or 3 lines of birds. They select birds from each line to breed that are more distantly related, such as aunts, cousins, etc. This also helps them to reduce unwanted traits and improve wanted traits and avoid breeding depression.
Not saying this is your issue, just something to consider.
This is a good point.
I'm ready this year to add outside cockerels to my flock this fall because Rameses is breeding his granddaughters now.
Fertility is fine, but I'm leery of creating problems.