Hello, i have experienced this too. 4 of my hens, out of six lay in the same nesting box. I only have 2 nesting boxes but i will get more quickly. One lays inthe box on the right and and 4 lay on the left. When the box on the right is empty, they still want to lay in the left bx. There is a gap in between the boxes and once i saw one of my hens trying to create a nest of her own in the gap by taking the straw. Although it will take her hours t make a nest by getting one straw at a time. Luckily i have never found a broken egg in the boxes, although i have found one broken by what i think was a bird as it was rollen and had a hole in it. I dont really have much to say which can help you, sorry