No results at all by a certain daterange

I search for a title of the the page ‘Bewijs van in leven zijn’ There is no results when I choose the daterange for exactly 3 months 01-07-2015 to 30-09-2015
When I Choose one day less there are results. Also when I choose a larger range as 5 months there are results, when I choose for 4 months there are no results. I can’t figure out why. The pictures show that there are visitors for this specific page spread during
Question: Why there are no results shown for three months if there are visits during that period? (see the images and specially the dates)