Even tho this was last hatch, Please Help

I wont be hatching any more till next spring (or maybe fall) but I just can't figure this out. My past three hatches were awful, losing over half of those that went into day 18. I blamed it on the unstable temps of my still air I was using for hatching. So this last batch I hatched I kept in the forced air preset bator, and expected great things...but no... same deal.

Of 11 in there at day 18 (all alive) 4 hatched. Today I opened the remaining eggs up. All fully formed, all dead. one of the 7 was slushy goop and didnt seem quite all the way formed. Another one of the 7 had broke into the air sac a tiny bit, then died. The remaining five, had their beaks near the air sac, but had not broke into it.

4 or 5 of these 7 had air sacs that seemed larger than usual. Is this the cause of the deaths?? If so, I know that is caused by humidity (I think) but dont know if it is from too high or too low humidity.

Any ideas whats going on here? Any questions I will try to answer. I feel like a genuine chicken murderer.

 

Yes, the eggs were shipped.