I think this macabre behaviour is naturally driven by a desire to clean up the nest and stop predators detecting nasty smells.He seemed to have been squashed in the shell & half stuck to it & then Wrold ate half of him... Really gross but I expect there was some nutrient she wanted from his carcass.
A 50% hatch rate is not uncommon, especially with novices. If they go broody again, they will probably do better.