If you have a water heater thermostat in a bator they have to be blown out with canned air or a compressor between hatches. Especially if you hatch in the bator the dust gets in the wafers and messes them up. I have fourteen EE eggs out of 19 still in the bator.
I also made sure to wash my hands well before touching the eggs to put them in - after losing so many to bacterial contamination the first time I'm taking no chances here.
Especially since I haven't candled since that second heat spike.