I doubt that one little humidity drop killed them. The two most likely causes of death in the two near term ducklings are bacterial infection or genetic abnormality in my opinion.
Thanks so much. That makes me feel a little better. I had wondered if I might have had bacterial issues all along. Out of 28 eggs that I set, 9 had no development at day 10 and when I cracked them open they all had a milky scrambled look. There was no discernible yolk...the entire inside looked the same. I wasn't sure if this was from shipping or a bacterial issue. I also had one start smelling that I promptly removed from the incubator. Another 5 had blood spots or rings and