The gap showing is due to the unevenness of the posted items in height. Not your fault though because of how this was coded. Unfortunately the only way to solve it is to use the same size thumbnails for each, plus have the same number of intro content lines so that each item is the same height. When one is a bit longer (taller) than the other, the next row gets obscured.
Starting Monday, I will be rebuilding the Preference theme from the ground up and the portfolio is going to be a much better one.