带CI_Sessions的Flash消息

I am having trouble with Flash Messages when $config['sess_use_database'] is TRUE. Whenever, it is FALSE it works without any problems. Below is my code and my configuration file. Why does it not work when I try to store the sessions in the database?

Configuration File

$config['sess_cookie_name']     = 'ci_session';
$config['sess_expiration']      = 7200;
$config['sess_expire_on_close'] = FALSE;
$config['sess_encrypt_cookie']  = FALSE;
$config['sess_use_database']    = TRUE;
$config['sess_table_name']      = 'ci_sessions';
$config['sess_match_ip']        = FALSE;
$config['sess_match_useragent'] = TRUE;
$config['sess_time_to_update']  = 300;

Controller

 $this->session->set_flashdata('item', array('message' => 'Record created successfully','class' => 'success'));
 redirect('dashboard');

Dashboard View

if(!empty($this->session->flashdata('item'))) {
  $message = $this->session->flashdata('item');
  echo "<div class='" . $message['class'] . ">" . $message['message'] . "</div>";
}