Chicks not fully formed

[Egg king]

Hi
I incubated some eggs but some chicks are hatching with their low body not fully formed and one was looking a bit ok in the brooder but after a while started bleeding and died eventually
Please can someone tell what could be the possible problem causing this

 

[EggSighted4Life]

Specific cause of embryo failure start around page 52..

https://www.hubbardbreeders.com/media/incubation_guideen__053407700_1525_26062017.pdf