You are doing fine- 16% layer feed is fine, frequent small treats of scratch or mealworms or kitchen scraps is fine, 2 roosters for 25 hens is fine. You have checked the ladies and their home for mites and I trust that you don't have a mite problem so that is fine. I also trust that your girls look healthy and happy, walking around, scratching and pecking, and acting like chickens, not sickly and lethargic.
I don't care if the days are getting shorter, or if they might be getting ready to molt, or if you are having an especially warm summer - 25 healthy, 1-2 year old hens should be giving you more than 6-7 eggs, a lot more, especially given your breed selection.
So I believe one of only two things must be happening - either they have found a hidden place to lay their eggs that you have not discovered yet, or something/someone is stealing your eggs. I doubt it is a hidden nest because the hundreds of eggs that would have built up over a relatively short time would be hard to miss in an enclosed coop/run so that leaves a sneaky thief. Are you able to set up a camera to catch the dastardly villain?