I know 30 weeks is young, but have you seen a lot of feathers flying around? Sometimes stress can cause a molt. I don’t think that cold by itself would be enough to cause a problem this wide spread, but did the water maybe freeze where they went more than a day without water? Did you maybe lose lights for a while? However unlikely you need to eliminate the possible. Molting is the number one cause for chickens to stop laying.
Number two cause is hidden nests. Just double check on that if you would. But after a month that nest should be knee deep in eggs. They can be pretty creative on hiding nests but there are limits.
Is something getting the eggs? Many critters (raccoons, skunks, possums, rats) would leave evidence behind, like egg shells or maybe a sodden mess. It’s possible the chickens themselves are cleaning up the egg shells, they will sometimes do that. But most critters are not that consistent. They will come in and take what is there but the hens don’t always lay at the same time every day. If it were these critters you could expect to see some days with good production, some with bad. It should vary, not be steady.
It’s possible you have a chicken that has learned to open an egg to eat it. The rest of the flock often joins in eating an egg after it is opened, that doesn’t make them an egg eater. It’s the one that opens the egg for them that is the problem. I had an egg eater once. She would only open about two eggs a day and a few of the other hens would join her in eating them once opened. They sometimes did not leave much egg shell behind but there were usually some bits and there was a soggy mess in the nest. I’d put this pretty low on the list of possibilities but it’s possible.
Some critters do not leave evidence behind. I think we can eliminate a snake this time of year. Besides a snake is not consistent. They eat what they can then stay away for a few days while they digest them before they return. I’m way too familiar with the pattern of a snake. You don’t have a snake problem, but I’m eliminating the possible.
Canines like fox, coyote, or dog will make eggs disappear without a trace. You still have the consistency issue, besides a coyote or fox would most likely be more interested in a chicken dinner. Some dogs however eat eggs but don’t bother chickens. Do you have a pet dog with access that has learned the egg song is an invitation to a snack? Not likely because of consistency but not totally unreasonable.
Another critter that will take eggs and not leave a trace is a human. Kind of creepy I know but it is a possibility.
Some chickens just shut down in extreme weather, whether the heat of summer or the cold of winter. It’s not just the lights but other factors are involved. Some pullets tend to lay throughout their first winter without stopping production but that’s some, not all. That cold snap may have been enough to put the brakes on for some. To me this is most likely unless you are seeing a lot of feathers flying around. They are just on strike until the weather warms up, then production should fire back up.
One other possibility I can think of, disease. Some diseases will cause hens to stop laying. Not all hens are always affected, some just have immunity. Normally when this is the cause they don’t just stop production immediately but you can get some weird eggs as the disease progresses, either shape or brown egg layers might lay white eggs. Also they usually act sick, lethargic, fluffed up, standing around and not active. If yours are not acting sick this is probably not it, but it is possible. I think I need to mention it.
That’s all I can come up with. Usually it’s just a matter of patience, frustrating as that can be. Good luck!
