That temp is actually high if there's a fan - if there's a fan in there, you'd want it to be 37.5 C. So it would make sense that your little one hatched early, because temps that are a bit high can cause early hatches.
My guess from what you've described is that the humidity is wrong. Late deaths in incubation are often the result of incorrect humidity. The humidity should be lower in the beginning of incubation, I find around 30% works well for me but that can vary, and then during lockdown you bump it up to about 65%.
My guess from what you've described is that the humidity is wrong. Late deaths in incubation are often the result of incorrect humidity. The humidity should be lower in the beginning of incubation, I find around 30% works well for me but that can vary, and then during lockdown you bump it up to about 65%.