Thought I'd toss out what I observed during MyABCs3's hatch in my RCom:
I hatched 5 other breeds at the same time, and had normal hatches with them. I did have a total of 8 IBs hatch (or partial), 3 of which survived. Of the 5 that didn't survive, 2 pipped and passed, and 3 burst out like popcorn, but with unabsorbed yolks or very raw umbilicus sites. One tore the yolk and I tied it off with thread, but it passed later that day. Another got very weak and just lay down. The third was mostly a raw umbilicus, but bled profusely and lasted 3 days.
I've never had a hatch quite like this, but would say it was a humidity issue if I hadn't had 15 other birds hatch just fine at the same time. It really was surprising with all of the other successful chicks all around them. This closely resembles what can happen in a styro incubator if hatching dark Marans or Penedescenca eggs if one doesn't use the dry incubation method.
I'm given to the idea that Iowa Blues may need a lower humidity for a better success- I'd be very curious to do an experiment and see whether I'm right!
The three that hatched well are huge, robust, active chicks, and seem to be growing very rapidly. I was kind of sad when MyABCs3 came to get them! ...like I need another breed...