Were the incubators close to each other? Its been documented that ducklings will speed up their development while still in the egg if they hear other eggs preparing to hatch.So, I threw some cayuga duck eggs in a couple days before my chicken eggs, separate incubator.
They are pipped. WHAAAA???
I found an article and posted it in this thread all about how chicks communicate with each other to coordinate their hatch:
https://www.backyardchickens.com/threads/really-interesting-article.1358854/
@MGG shared her first hand experience of this happening too - really amazing.