В шестёрке при подключении к базе тоже utf8mb4
/*
-----------------------------------------------------------------
Подключаемся к базе данных
-----------------------------------------------------------------
*/
private function db_connect()
{
require(ROOTPATH . 'incfiles/db.php');
$db_host = isset($db_host) ? $db_host : 'localhost';
$db_user = isset($db_user) ? $db_user : '';
$db_pass = isset($db_pass) ? $db_pass : '';
$db_name = isset($db_name) ? $db_name : '';
$connect = @mysql_connect($db_host, $db_user, $db_pass) or die('Error: cannot connect to database server');
@mysql_select_db($db_name) or die('Error: specified database does not exist');
@mysql_query("SET NAMES 'utf8mb4'", $connect);
}