Frequently the breeding vigor and frequency is decreased as well a there being diminished sperm in the ejaculate. All these can produce infertile eggs. The weather plays some role in this. Colder, darker periods accentuate the problem. Eggs which begin developing but fail to fully develop and die in the shell can be the result of several things.
Poor incubation can cause embryo death.
Eggs getting jarred excessively at critical points of development may also perish. Infection in the egg is probably the most common cause. The infection may be incorporated in the egg by hens having an oviduct infection. Infection more frequently occurs through the shell. This can happen during laying as they often become contaminated with feces during this process.