It has been suggested that it was incubation related..
Re incubation - they were @ 89.1f for 59 days before hatching - i'd be inclined to look at that more closely except all the other eggs in before/at the same time hatched totally as expected.
Others have suggested a hidden gene.
Mum looks fire-ish, the pic of her is her in heavy slough but she has nice bluching, nice yellow markings and a fire look to her.
Certainly something to play with. I'll keep a male to put back to mum at the very least.