Hi,
The problem comes from the image "Birchen Ayam Cemani" which doesn't have the same ratio as the other images and the fact that you have the "force size" option turned off.
Because of that, the box of that product is bigger than the others and the columns system doesn't work properly.
Forcing the height in CSS is a solution (and you can restrict the height forcing to only some screen width with the @media of CSS (
css-tricks.com/css-media-queries/
), but I'd rather recommend to have the same ratio for that image.