I would think about their age...my first batch gradually stopped laying around 2 years or so.
I also would think about do you leave the coop open while they free range? (I found out my dog was getting in the coop while they free ranged and was getting eggs).
So my next question is do you have a dog? (My dog looks too big to get in the coop but she can.
I also made a point to check my coop every time the "egg" song stopped. (because of the above naughty dog)
Are they molting
Is the weather getting colder for them.
Just a few things to think about.