Duck egg stopped developing/died?

[Callduckies]

I'm wondering why two out of seven of my call duck eggs in the incubator died? I would guess they were somewhere between 8-12 days old when they stopped developing. The rest of the eggs look totally fine and I've hatched two other batches of eggs and no dead embryos. Is it just something that happens occasionally?

 

[oldhenlikesdogs]

It does just happen. Not sure why.

 

[Ridgerunner]

I'll link a couple of troubleshooting guides. They will show you some of the things that might have caused them to stop developing at that age.

Trouble Shooting Failures with Egg Incubation | Mississippi State University Extension Service (msstate.edu)

Common Incubation Problems: Causes and Remedies (ucanr.edu)

Most of these will probably not make much sense since it is only 2 out of 7. Sometimes I get perfect (100%) hatches. Occasionally I get a hatch where different eggs stopped at widely different times, I can't pin it to any one thing.