By default the Toggle mobile menu style uses the javascript slideDown animation but it can be disabled with a little code. When disabled the show/hide functionality will be done via the "visible" classname instead so you can apply custom CSS animations if you wanted or no animation at all.
add_filter( 'wpex_localize_array', funtion( $array ) {
$array['animateMobileToggle'] = false;
return $array;
} );