Aww, glad I could help. :) Sorry about the babies, though--what a disappointment. It happens to us all at some point, of course--I had it happen once because I had a batch of bad quail eggs in the same incubator and didn't realize that they were filling the bator with humidity (and probably...
Since they were all alive at Day 20 and then didn't hatch, my suspicion is that your humidity was too high during the main portion of incubation (I'm not talking about during lockdown, but rather during the earlier portion).
Late deaths like this are very often caused by an air cell that did...