If you have activated the theme with the existing content, you will have problems with grid layout.

Once it's activated, our theme generates necessary thumbnails for every newly uploaded image. Since these were uploaded prior to activation of the theme, thumbnails do not exist yet.

In order to correct this, please install the following plugin: Regenerate Thumbnails and run it. Once you do that, all necessary thumbnails will be regenerated and the issue should be resolved. All newly uploaded photos will be ok.