How to tell what went wrong by an eggtopsy

[WhiteTreeOfGondor]

My first Ancona duck hatch this year is not going very well; only 10/22 were fertile, and now I am down to only 5 living eggs on day 12. Out of the 5 that died, 4 were from the same duck so all of her eggs have now died. I am wondering if it has something to do with her specifically or maybe her pairing? She laid quite large eggs too, I don't know if that has anything to do with it. I cracked open her 3 eggs that I found dead this morning but I have no idea how to tell by looking what went wrong. Is anyone able to tell by pictures?
Thank you!

 

[Yardmom]

How did you determine these eggs were dead? What are the ages of your ducks? How old were the eggs you set? Did you confirm that the thermostat and hydrometer were reading correctly (use extra thermometers ect to check)

 

[WhiteTreeOfGondor]

I could tell they were dead when I candled them because there were no veins, just cloudy dark contents swishing around.

The eggs would have been anywhere from 1-7 days old. I collect them for a week and store them in a wine cooler until I have enough to set.

The particular duck whose eggs all died is about 10 months old. The others range from 9 months to 2 years.

I do have a Govee thermometer/hygrometer in the incubator. It always shows that my incubator runs low, so I keep it set to 100°. I was having a bit of trouble with the temperature going up and down within a couple degrees since our weather was alternating cold and hot, and we use our thermostat sparingly. So that could have been the problem, if the fact that all of that duck's eggs died was just a coincidence.

Also, she could be is more closely related to the drake than I thought. I thought they were half siblings but if they are full siblings, maybe inbreeding is the problem.