Display products randomly by default on the shop page in if using WooCommerce on your child site.
Snippet Type
Execute on Child Sites
Snippet
add_action( 'pre_get_posts', 'shop_default_orderby_rand' );
function shop_default_orderby_rand( $query ) {
if ( is_shop() && ( ! isset($_GET['orderby']) || 'menu_order' === $_GET['orderby'] ) ) {
$query->set( 'orderby', 'rand' );
}
}