Bad news. The other chick is dead.

I candled the egg this morning and it was obvious. I did feel I needed to know what happened though because it certainly had nothing to do with a blood circle and I think I might.
I'm going to describe in detail what I found when I opened up the egg. I need your help in determining what might have happened so I can hopefully fix it before my next 2 go into lockdown in a couple of days.
Last year I lost one of my chicks after it started trying to pip and failed. The yoke sac on that chick still needed to be absorbed.
Although this chick hadn't totally absorbed its yoke sac either it was very near. Other than that it was fully developed. To me, there was no doubt it suffocated. The question is why.
One thing I noticed is its head was still tucked down away from the air sac. It showed no signs that it ever moved from that spot. The chick also seemed too big to maneuver. The air sac was extra large at this point but it wasn't that way when I checked 2 days ago so I was thinking that it might be from gases released after it died even though I saw no decomposition as of yet or it really was the humidity.
The other thing I noticed is that the membrane was rubbery and thickish. Again I don't know if that happens after a chick dies or not but if it doesn't I would say the chick would have had a difficult time pipping through.
From what I've read in this forum it sounds like a humidity issue. Last year I kept the humidity at around 70 or slightly above during lockdown. This year after searching for the best humidity during lockdown I kept reading 60 - 65. You might also remember me having trouble with my hygrometer where the humidity would take a plunge shortly after I would get it stable.
I'm sorry if I was too detailed above. I've always thought too much information is better than too little.
Thanks everyone.