If you have a ‘grid’ theme (more than one post column) you make notice a gap at the end of your posts… or in the middle if you have infinite scrolling. To rectify this, you need to change the number of posts per page to a multipy of the number of post columns. For example, if you have two post columns, change this number to either 2, 4, 6, 8, 10, 12…. etc.

How to change this number:

Go to customize > advanced > change the number i’ve highlighted