Why did this chick die?

[LongRanch]

Yesterday was day 18 and we candled before lockdown -- we noticed that a handful of the chicks already had their beaks in the air cell, pecking the shell and peeping. My husband woke me up at 3am to tell me that one of them was already pipping. Sure enough, there was a hole with a beak sticking out, and it was peeping. I went back to bed and got up at 6am, and the pipping had not progressed, and the chick was quiet and there was no movement. After looking for several minutes to make sure it wasn't just taking a break, I took the egg out.. Yes, dead chick. Opened it up and the chick was perfectly formed, nothing wrong with it. It was maybe a little sticky around it's head where it was most exposed to the air, but the humidity was at 68%. It had pooped in it's shell. It's crop looked big -- is that normal? Any ideas? Temp was perfect at 100 degrees. I have one more pipping as we speak. Should I be changing the humidity?

This is our first successful hatch so we were pretty excited when we candled lastnight -- now I'm a little worried!