Front page display problem

I’m using the “Alternative Layout” for Zillah. When viewed from a computer, each row should have 3 articles, but in the 3rd row, the leftmost article is missing (there is a blank), and in the 4th and 5th rows there are only one article on display on the left, while the middle and right blocks are blank. How may I fix this?

The page I need help with: [log in to see the link]