I just finished my first hatch on Tuesday. Out of a dozen eggs, eight hatched. The four that didn't make it must have died during, or close to, lockdown. None of them had pipped the shells.
Three of the four deaths were probably related to issues with my (homemade) incubator. It had held temperatures pretty steady throughout the first 18 days. Before lockdown, I added a hardware cloth barrier to separate the eggs from the lightbulb, thermostat, and fan. I also made a foil "shield" to place in front of the light, but ended up removing it because the reduced air circulation was causing major temperature swings, and I was worried I'd lose the entire batch. (Before lockdown, I would rotate the eggs' position in the incubator, in addition to turning them, so no eggs would sit directly in front of the light for too long.) It seems like no small coincidence that the three eggs in the row closest to the bulb didn't hatch.
The first chick was malpositioned in the shell, with its beak kind of wedged down between its thighs, and its feet over its head. The inner membrane seemed gummy to me, though I don't really have a point of reference for what it's supposed to feel like.
The second egg was wetter. The spots of orange make me wonder if the yolk sac may have ruptured while the chick was trying to position itself.
The third egg seemed similar to the first, so I did not photograph it.
The fourth egg, which was farther back in the incubator, looked a little different. It, too, was rather wet, with a very strange yolk sac with dark, black-ish coloring. Can anyone tell me what this is about? Are these organs?
From the other side: