I have no idea whether what we call "ovulation" and "follicles" are really correctly labeled. I've never bred ball pythons and have never considered that I have successfully palpated any of the snakes I have bred.

An egg cell develops inside a follicle and cannot be fertilized there. Once the egg leaves the follicle, it can be fertilized. The egg shell forms around the egg. Sperm cannot get through the egg shell. Either the shell contains a fertile egg which will produce a hatchling (if all goes well) or an infertile egg (a slug).

When you crack open a chicken egg, the yolk is the actual egg cell. That is what leaves the follicle in the ovary. Most of the chicken eggs we buy in the store are not fertilized, though.

IMO, if the homozygous spider genotype is lethal, death happens sometime between the egg leaving the follicle and sexual maturity of the hatchling. There might be some fault that prevents the spider sperm from pentrating the spider egg, so a normal sperm wins the seminal sweepstakes. Or death could happen after fertilization. Your guess is as good as mine.