Sorry to hear that. Hope you have better luck with any other clutches.
Last season we had a clutch of 4 slugs and 3 eggs. Turned out 2 of the eggs were infertile. Only got one viable egg. This year a different girl laid the same ratio of slugs to eggs and one egg died a few days ago. The embryo was starting to develop. Two good eggs from that clutch. So far I've had crappy luck all around.