HELP! I cracked an egg at 25 days as i thought it was a dud

[ChirpyChicks1]

 

[nconley11]

So I let the other egg go like 10 more days. Same play date and I finally cracked it open and it looked like it was fully developed like the other one was but it was dead. Do they typically not sit on them towards the end? I found it not being sat on so I moved it underneath another hen and I'm wondering if the chick got too hot? Any recommended reading material for letting Broody hens hatch eggs?