Sorry to see this. Was the egg resting up against the side of the egg tub? Do you think it was a moisture issue like condensation dripping onto the egg? What was the pairing? Are the temps and humidity stable and have you had any fluctuations in your temps (spikes, low temp)? Does the egg smell bad? I would consider putting the eggs on a light diffuser if you haven't already and keep an eye on any progression of the discoloration/ excessive dimpling. Good luck.