Wordpress chyba pri upgrade na 4.9

Warning: preg_match(): Compilation failed: unrecognized character after (?< at offset 4 in /***/public_html/wp-includes/wp-db.php on line 1657

* @since 4.9.0
    *
    * @param string $host The DB_HOST setting to parse.
    * @return array|bool Array containing the host, the port, the socket and whether
    *                    it is an IPv6 address, in that order. If $host couldn't be parsed,
    *                    returns false.
    */
   public function parse_db_host( $host ) {
      $port    = null;
      $socket  = null;
      $is_ipv6 = false;

      // We need to check for an IPv6 address first.
      // An IPv6 address will always contain at least two colons.
      if ( substr_count( $host, ':' ) > 1 ) {
         <strong>$pattern = '#^(?:\[)?(?<host>[0-9a-fA-F:]+)(?:\]:(?<port></strong>[\d]+))?(?:/(?<socket>.+))?#';
         $is_ipv6 = true;
      } else {
         // We seem to be dealing with an IPv4 address.
         <strong>$pattern = '#^(?<host>[^:/]*)(?::(?<port>[\d]+))?(?::(?<socket>.+))?#';</strong>
      }

      $matches = array();
      $result = preg_match( $pattern, $host, $matches );