How can I get session at multiple controllers

Hi,
I set SESSION at Login.php controller, And I want get SESSION at other controllers,
But at other controllers, I get SESSION have `__ci_last_regenerate: 1552555932` only, No information I have stored in it.
What can I do something get the SESSION?
Thanks!

This is my Login.php controller

PHP Code:

class Account extends CI_Controller
 {
  public function __construct()
  {
   parent::__construct();
   $this->load->model('Account_model');
   $this->load->library('session');
  }


  public function login()
  {
   $username = $this->input->post('username');
   $password = $this->input->post('password');

   // run login model,return array or FALSE
   $query = $this->Account_model->login($username, $password);

   if ($query) {
    // set SESSION
    // $query is array, like this :{'username'=>"bob",'level'=>2}
    $this->session->set_userdata($query);
    //do something...
   }
  }
} 


And this controllers, I want use SESSION, but faile

PHP Code:

class Number_record extends CI_Controller
{
 public function __construct()
 {
  parent::__construct();
  $this->load->model('Number_record_model', 'NRM');
  $this->load->library('session');
 }

 public function add_num()
 {
  // I want get SESSION at this
  // But only get this :__ci_last_regenerate: 1552555932
  $_SESSION;
  $this->session->userdata()
 }
}