Check for egg loss from rats..this is the time of year many report egg loss and are even finding empty shells in the coops. Mostly, though, you won't find evidence as they merely steal them and store them in their nests to be eaten at their leisure. They can steal an enormous amount of eggs, depending on the colony numbers.
The ages of your birds would seem to suggest they should be laying well, both groups. One way to know who is laying and who is not is to do a digital exam at night, taking the birds off the roost. You should be able to palpate the next day's egg in the oviduct, through the intestinal wall. This will let you know if they are actually laying but you are not receiving the benefit of it.
You could try an experiment....go back to feeding dry feeds for a few weeks and see if that makes a difference. Then, even if it does make a difference, switch to FF again for a few weeks and see if you note a decline. It would be interesting to know if the FF is slowing your egg production down, though no one else is reporting that...usually just the opposite.
I've noticed one thing through the posts on this thread....birds that normally come into lay at 4-6 mo. seem to be taking a little longer to come to sexual maturity and I'm wondering if that has something to do with the FF altering the soy proteins in the feed. Soy protein has the advantage~or disadvantage, depending on how one sees it~of stimulating more of the chicken's natural female reproductive hormones than would normally be produced if one was using a different source of protein. This has shown up in medical studies done on young girls who consume commercially sourced animal products and the relative ages they start menses compared to when girls used to start. It also has shown up in the young boys as causing more feminine characteristics due to the stimulation of the wrong kind of hormones, causing the boys to gain more weight in their breasts and hips where girls would normally gain and causing a general lower testosterone level.
It's a thought. Not a fully formulated one but it's still a thought.