And you've watched the flock all day - no breaks?
I've had very abnormal things happen with egg laying. For about a week, I had a Jaerhon hen fly out of her pen, only to fly into another pen where she was persecuted, just to lay an egg in that nest.
I only witnessed it twice but she laid white eggs and all the hens in the pen she flew into laid very dark eggs. There was a white egg in that pen's nests every day for the week. I don't know how she knew there was even a nest in that building since she had never been in there, nor I know why she quit the habit.