I've attempted hatching duck eggs twice in the last few months. Both times I've started the duck eggs, 7 days later, add chicken eggs to the incubator. The ducks pip at day 24 or 25 and need help getting out of the shell. I've monitored temp and humidity and are spot on. Chickens hatch on day 21 as expected. Something goofy with my duck eggs. Anybody have an idea as to what may be happening?