One chicken hasn't layed in two months

[Luddy]

I recently got 4 isa Browns at the beginning of April that were at point of lay 19 weeks old I brought them home and by the end of the first week I was getting 4 eggs every day each egg a different shade and every morning the same 4 eggs until May 4 since then I have only been getting three eggs every day I have been missing the med shaded brown egg and it's going on almost over two months and nothing. But the other three have layed the whole time not missing a day yet. They are in an enclosed coop and run with top and everything so it's not possible that the eggs are being layed any place else, they all seem fine and stick together three on purina layer feed with flaxseed and oyster shells on the side. I can't see any signs of moulting or broody and right now they are all only 30 weeks old. I guess I'm just wondering if anyone else knows anything I'm not thinking as to what's going on is it normal for a bird to start laying for the first time for a month then stop for over two months, is it possible she will never lay again. I just keep my hopes up every morning

 

[crash0330]

Do you know exactly which hen is not laying?
Could it be possible that maybe they are all laying, I mean even Isa brown hens have to skip a day in laying almost every week. Although egg color stays pretty consistent, they can lay different shades of their original egg color, specially during times of stress, like moving homes or heat.
It could also be the summer heat making them slow down.