Eggs gone bad?

[Meltdown Morphs]

Some pics would help, but it sounds like a baby may have died in the egg.
Being that far along something may have happened to the hatchling, tangled umbiclus, severe deformities, maybe drowned ,who knows.
If your certain you know which eggs are causing that odor then I suppose you could remove them and cut them open to see what happened or if they are still alive perhaps.