chobson

Got some great advice elsewhere from someone better at this than I am (Howdy_McGee), basically I was returning a single page, when I should have been using if( ( is_page() || is_home() ) ) { and calling a global $post ID will not work so that’s replaced with $blog_id = get_option( 'page_for_posts' ); works like a charm!

//* Add Header Images on Posts/Pages
add_image_size( 'header-img', 1600 );
add_action( 'genesis_after_header', 'site_banner', 0 );
function site_banner() {
    if( ( is_page() || is_home() ) ) {
        $post_id = ( is_home() ? get_option( 'page_for_posts' ) : get_the_ID() );

        if( has_post_thumbnail( $post_id ) ) {
            $ftbanner = wp_get_attachment_image_src( get_post_thumbnail_id( $post_id ), 'header-img' );
            $banner = $ftbanner[0];
            echo '<div id="site-banner" class="site-banner">' . "\n";
            echo '<img src="' . $banner . '">' . "\n";
            echo '</div>' . "\n";
        }
    }
}

Noob move, didn’t re-upload the SQL file to the new host.