Where is Wilton to Iowa City?
ETA: You're pretty close to me. I work at the U of I. My sis has a black Roo on Wheaton based Ameraucana hens (offspring would be black). One hen is laying a nice big blue egg (roo is from blue only line so eggs would be blue from this cross). I'm getting 100%...
I always go by wet bulb readings. 84-86 degrees wet bulb for incubating, 90-91 for hatching.
Looks like you are at about 81 degrees for incubating and 88.5 for hatching, that could be the cause for late hatch/late quitters.
How big are the air cells on day 18?
Most of my experience has been...