Beer Can --
Bummer! Was there enough air/oxygen in the incubator during lockdown? I've had "launch pad" failures with shipped Marans eggs and a few others. Low-altitude laid eggs not getting enough air through their pores when attempted to hatch at a higher altitude. The ones that did manage to hatch were definitely, err, physically and mentally challenged and disposed of.
So sorry to hear that your chicks were so close. That's heartbreaking.
Good point. Good ventilation is often overlooked!