Fertilized chicks dying in the shell

[GrandmaCyndi]

I have an 18 egg incubator. The last 3 hatches I've done I get 1/3 hatched and healthy, 1/3 ended up being unfertilized and 1/3 formed but died in the shell.
These are all from my own chickens, not bought or shipped and all less than 10 days old at incubation.
Any ideas on why chicks are growing but dying before hatching?

 

[Tex452]

How many hens/rooster do you have?
Do you live in a high humidity area?
I got eggs from my son that has a good hens to rooster ratio, I hatched 20 out of 21 fertile eggs.
I got eggs from a friend that had 1 rooster on 27 hens, I got 8 fertile eggs out of 22 eggs, all 8 hatched.
I live in a high humidity area, and I do the 100% dry hatch method, no water added at any time, so far I have a93% hatch rate or a little better.
I hope this helps.