**What I did worked for me but may not work for you. I'm not an expert.
The first incubation went well. 6 of 7 hatched. The 7th one got a beak through the shell and then did not make any more progress and died. Wanting to know why I took the shell apart a few days later and saw a fully formed, large chick inside. I read up chick in shell death and one article mentioned that large chicks may have a problem getting out of the shells. It is easier for a small chick to get out.
The second hatch also went well. Until the 5th chick tried to hatch. It got it's beak through but that was all. I waited until about 10 -12 hours later and still had a peeping but no further movement in the shell coming apart so I picked up the shell and started to dismantle the shell. Carefully. Pieces came off but the membrane stayed intact. After awhile I pinched the membrane open (scared the chick) and left it in the incubator. Within a matter of minutes the chick was out. Eggs 6 and 7 were not fertilized which is why they did not hatch. (I'm not good at candling).
We are towards the end of the third hatch. Egg #6 had issues. Part of the shell came off but the membrane was intact. So I waited. About 14 hours later still no progress but the chick was peeping. I started the dismantling process. But this time there was blood (from the membrane I later found out). So every time the egg started to bleed I put it back into the incubator. I also wet the membrane with a slightly damp paper towel so the membrane didn't harden. I kept this up for awhile and eventually had to open the membrane. A chick slid out and laid there. But it was breathing. So I left it in the incubator. About 3 to 4 hours later it was walking around and I cleaned off the blood (so the other chicks would not peck at it) and put it in with it's siblings. The chick is the one on the bottom left. It is walking around fine, chirping, eating and drinking.
**When it came out of the shell it's head was tucked inside in a way that it never could have reached the membrane to break it
Egg 7 might be another dud.