Ok, it shouldn't be day length, unless maybe the coop is really dark and they get locked in early or late, that seems unlikely.
So, molting, broodiness, daylength, breed, and general health are at least tenatively ruled out.
That leaves hiding a nest; less likely if she is seen in the regular nest but sometimes she or another hen will move eggs out of a nest.
Predation; have you checked for signs of snakes, opossum, skunks, ect - or even just gaps in the floors, walls, fence and such?
Egg eating by the chickens; I haven't had an egg eating chicken but I think they usually leave a mess although not always.
Is there any other person who could be gathering eggs? Such as miscommunication among family members, someone playing jokes, someone stealing eggs? Are other hens laying as expected?
Can you tell which eggs are hers? I thought I could tell my Mocha's eggs because her's usually have speckles and none of my other hen's eggs do. Than I learned a given hen can lay specked eggs or not.
Stress. Such as heat stress or dehydration.
If none of these seem to be the problem, it could be worth taking a closer look at each - some can be quite subtle even if they often are not subtle.