Hens Laying in Random Places

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My hens have recently started laying in all kinds of random places (both in my bantam coop and the coop with the large hens). They were all laying perfectly in the nest boxes, but have recently started laying all over the place: in the nest boxes (great!), in the floor of the coop (not so great), and on the ground in their runs (even less great). One even laid in the middle of the yard when they were free ranging one evening! I don't know what started this as they always used the boxes all last fall/winter and this past spring. Does anyone have any suggestions on how to get them to reliably go to the next boxes again? For reference, my bantam coop has 2 nest boxes for 4 hens. My standard hen coop has 3 nest boxes for 6 hens. Also, the problem seemed to start after a few of the hens were moved back to their respective coops after having been in separate pens for a while doing the broody thing.