Chicks dying just hours before hatching

[Jessicx]

3 out of 7 chicks passed away yesterday, seemingly hours before hatching. One chick had not absorbed its yolk, so cause of death was pretty clear. However, the other two were fully developed. One was really wet when I opened the egg. The other seemed almost the opposite. The membrane on the airsack side was really dry. Can anyone offer clues so that I may prevent this from happening again. Lockdown humidity is between 60 and 70 percent, temp at 99.5. Humidity prior to lockdown is 40 to 50 percent.
Also, I used to set my eggs one at a time. Eventually, I started collecting them and setting them after 7 days. The ones I set individually ALL hatched. But, the of the stored eggs, only about 60% have hatched. I store them at around 50 degrees, and they get turned three times a day. They all start out just fine, but something is going haywire at lockdown.
Thank you all for any help you can provide!!!

 

[AlleysChicks]

Do you mark your air cells when you candle? That may help tell with the wet and dry chicks. (Too little ACs or too large) The chicks also may be getting too big to zip if they were wet... I've had that happen a few times. They were fully formed but too big to get into position to pip.

 

[Jessicx]

Do you mark your air cells when you candle? That may help tell with the wet and dry chicks. (Too little ACs or too large) The chicks also may be getting too big to zip if they were wet... I've had that happen a few times. They were fully formed but too big to get into position to pip.

I used to, but I began to realize that it defeated the purpose of lockdown. The aircells on these eggs looked normal, and were positioned well. I do agree with you that the birds might have been too big, as neither one of them were in a position to pip through the aircell.

 

[Jessicx]

Ok guys, need more help!!! This new clutch has started hatching yesterday. Last night, I helped one out that had stopped breathing. It took one last breath after hatching, and was gone. It had not absorbed its yolk. As second one was again "stuck" to its shell. I finally decided to help after it has stopped progressing for 24 hours. Half the shell membrane was stuck to this baby! This is really becoming a problem. Any ideas?????