(May be advanced) Need help with rows of posts…

Pastebin: https://pastebin.com/fJN0JAVQ

I am having trouble with the above code, when I only display 4 posts on the index page then the end result is fine, with both rows showing 2 posts, images in line etc.

However, when I choose to display anything above 4 posts only the first and last row displays two posts, with the rows in between all showing one.

The CSS can be found here: https://pastebin.com/rTyRfwE4, though I imagine it is more of a PHP problem than it is a CSS one.

Any help on this matter would be hugely appreciated. Thanks in advance.