Using Show Posts shortcode destroys GP layout

Hi, I'm trying to use Tom's WP show post on the homepage of this site I'm working on.
Without the shortcode in the body, it shows as a blank homepage.
As soon as I place in the shortcode, the site structure falls apart.

I tried this using sections by placing the shortcode in a section and in the regular WP editor. Either way, as soon as the shortcode is in place, the template goes awry on the frontend.

Any tips or help is appreciated.