Can you wipe the egg off and candle it again to see how it stands? How is the smell?

There are two types of moldy eggs, those that candle good and have high chances of going full term and those that no longer have veins (those will develop a very foul smell), those are obviously dead.

It's sad but it happens, the more clutches the more likely you will be to encounter slugs, eggs dying and worse. Sometimes some eggs are just not meant to be, I had clutches where all the eggs but one went bad so it happens for no apparent reasons.