I think it is connected with the coding in the theme.  I am using Woocommerce in the same manner on another author website and I am NOT getting this error.  If you will see the guide that you referred me to, you will see at the bottom it references problems with the exact error code I am getting under the heading “The Additional Information Tab.”  
In functions.php of the Shogun theme, you have included this snippet, which IS the additional information tab:
//// Rename product tab
function shogun_sd_wc_rename_tabs( $tabs ) {
	$tabs[‘additional_information’][‘title’] = __( ‘More Information’, ‘satori’ );
	return $tabs;
}
When I delete this snippet of code, then hit save, I get a 418 error.