What's wrong with my eggs?

[Rhacodactyl]

I've had an egg go through an odd change this last week in two different clutches in separate containers. Each of them have collapsed noticeably as if dried out, but they're also growing mold. The humidity levels should be fine and the other egg in each clutch still looks good. I would assume they were infertile, but each one has a healthy white shell and one of them has been incubating for almost 2 months now with no visible changes. Any ideas?

 

[Mel&Keith]

Sometimes the embryo dies and the egg goes bad. There's no way to know exactly why, it's just that something wasn't developing properly.

 

[GeckoRing]

Sometimes they start to collapse just before they hatch.