As far as the drastic egg count reduction, the first thing that crossed my mind is snakes. Your temps are cool in the mornings, but plenty warm enough by the afternoon for snakes to find the eggs. I would try gathering at least 2x daily for a short while and see if you get more eggs. Large snakes like the one below eat 4 eggs each and every day, and often there is more than one. Every time I have a drastic drop in egg production, I know a snake(s) has discovered the nest boxes.