I love the vast array of breeds you have. You aren't giving them a balanced diet, cut back on grains and corn. An average hen eats about 1/2 cup food daily, adjusting for size - bantams less. I have 102 chickens, ducks and guineas, they go through 4 - 30# feeders (filled 2x weekly) in one coop and 1 - 30# feeder in another coop weekly which is about 200-250# of feed (1 50# bag of pellets fills 2 - 30# feeders) . I also have juvenile chickens and ducklings that get "All Flock" pellets 50# weekly or "Flock Raiser" crumbles 50# monthly depending on ages. Mine are free fed the layer feed and I keep an 11# feeder of oyster shell available at all times that is refilled monthly. I don't give any treats until noontime, once they've had layer feed first and it's about 4 cups spread between all except those under 8 weeks. They might get black oil sunflower seeds one day, scraps another day, or I also buy manager special veggies and packaged greens (1 bag divided between them) to mix things up. Now with a garden growing, we give them all the weeds every evening, especially to the ducks about an hour before sunset (most chickens are roosting by then). I have a total of 4 coops with a 1025sqft uncovered pen in summer, 2,050sqft when there's no garden. Plus a 5th coop with 125sqft covered pen (4 guineas, 5 hens and 2 roosters). My 42 hens range from 8 months up to over 4 years and I get an average of 22 eggs daily not including duck (3-6) or guinea (1). I have a few broody hens too that I keep removing from nests. Heat seems to have a lot to do with their laying as its been in the 80's pushing 90 at times with higher humidity and more than normal rain this year. Also the breed makes a difference on laying too, some lay 6 even 7 days weekly, while others lay 3-4 times a week. I have all large breeds, my last bantam, a Showgirl, passed January 2020 and she laid 3-5 times weekly until a week before passing.I agree about the light. I hadn't thought of that. Would you recommend artificial lighting?
I think it's not hot enough to reduce laying.
The secret nest thing, it's possible. I've had it happen before when my chickens would fly out. But now we have netting over both runs to stop them. and after we let them out, we watch them, so most likely, that's not it.
Also about the molting, that was one of my ideas too, but none of them are showing signs of it.
I have lots- and I mean lots- of different kinds:
Roosters:
Golden Sebright bantam
Barred Rock
Buff Cochin
Silver Duckwing OEGB
Golden Laced Wyandotte
Hens:
Barred Rocks
Golden Sebright bantam
Blue cochin bantam
Black cochin bantam
Golden Laced Wyandotte
Black Sex Link
Maran
Crevecoeur
Lakenvelder
White Crested Black Polish
Black Jersey Giant
White Leghorn
White Silkie
Buff Cochin
Black Breasted Red OEG
Ardenner {Ardennaise}
I have RIR, Easter Eggers, Cuckoo Marans (light and dark), Amberlinks, red sexlinks, golden comets, buff Orpingtons, Jersey Giants, buff and light Brahmas, Welsummers, Speckled Sussex, Australorps, and a few more not remembering hens. Roosters are 3 RIR, 1 Cuckoo Maran, 1 Amberlink/black Australorp, 1 buff Brahma and 1 Easter Egger. I've got 35 juvenile chicks that are yet to be known, most bought as "sexed" pullets but my last group of 6 pullets only had 3 pullets, hence my Easter Egger rooster.
Try cutting back on treats. They should only get 10% of they're diet from treats or scraps.