I just went through similar with mine. The first one I had start to lay refused to use the nest boxes. Instead she made a nest in the dirty shavings under the nest boxes. I finally decided to block off the area so she couldn't get to it. Well, she laid one egg in a nest box then stopped laying. That was about 6 days ago. Yesterday I changed things up, put a large cat litter pan under the nest boxes for her to use a s a nest (I don't care if she lays there, I just can't find the eggs under the boxes, so with the litter box I can pull it out if it looks used). Well, I am pretty sure she has now decided the nest box is just today because she (I'm 95% it was her) laid in a nest box today! LOL.
Not sure if I did the right thing or not by blocking off where I didn't want her to lay but, it may be an idea.?