I feed my hens lay crumble, lots of scraps, and chicken scratch. When I run out of crumbles, seems they lay less.
Maybe your hens are on strike, hmmm, keep them locked up and give it more time. Try some lay pellets or crumbles maybe?
Give them a couple more nest boxes. I use old drawers, old cat carrier crate, anything that is a box.
I usually put hay in my boxes, sometimes I have shavings.
We have three - Rhode Island Reds - I will try a new nesting box tomorrow, will keep them locked up a few days and see what happens. I'll report back in a few days.
Locking them up for a week in the coop sounds like a good thing to do. Add some golf balls to the nest boxes to show them where to lay eggs. Do you have any pictures of your coop and nest boxes? We might find more clues.
I'm having the same problem with 1 year old ladies that we moved out of the barn coop into the tractor. We butchered 3 roosters that were pestering them and my children. 2 New Hampshire Reds and 1 Dominique. We were hoping that after we killed the extra roosters, and put them in the cozy tractor they would go broody. They hated not having their nest boxes, since that's where the new chicks are, there's no access. We found a couple hidden eggs, and some with no shells, but now there's none! We're adding oyster shells to their feed. Is it the stress of being kicked out, or is our rooster of choice not up to snuff? We feed organic grains and leftover buggy food from my natural food place of employment. They free range all day. I may try and easter egg hunt, then I may put a nest box in the tractor and lock'em up!
I'd take out freeranging until I got an egg. I hate when my girls freeload, especially since I only got 2 hens. Check their vents and see if they look like they are still laying.