F2 Lethality

Hi all,
I crossed EG8040 with another strain, and found F2 progeny died on the NGM plate. Could someone please tell me possible reasons?

Here is what I did:
Day 0, cross EG8040 males and other hermaphrodites in one NGM plate
Day 3, single F1 progeny with EG8040 marker
Day 5, check self-cross F2 progeny from F1. So far, F2 and F1 are all looking good.
Day 6, all F2 and F1 died on the plate. The worm size and stage looks the same as Day 5.

Before, I found my cholesterol crystallized out ( don’t know why, I dissolved 10mg/ml cholesterol in absolute alcohol), and accidentally grew my worms on these cholesterol deprived plates. But I have transferred these worms to the normal NGM medium. Could this have anything to do with F2 lethality?