Codeigniter 3.0.3 sessions are not persistent

I am having very weird problem, The sessions in Codeigniter 3.0.3 are not saved for next request. Each time when a request is done, it creates a new session record and doesn't use it next time.

The weird part of it is, it does work on HTTPS version of website, but not HTTP.

The scenario: On the login page of my website, I do an AJAX call (on this call I set some session variables and flashdatas). Once I get success message, I reload page to the profile page.

This whole process don't work when I use HTTP, but HTTPS.

Any help would be appreciated.

EDIT v1: Addition, even CSRF doesn't work over HTTP. I disable it to test the system.

EDIT v2: Code requested by @DFriend

config.php

$config['sess_driver'] = 'database';
$config['sess_cookie_name'] = 'jupiter';
$config['sess_expiration'] = 0;
$config['sess_save_path'] = "hkr_sessions"; 
$config['sess_match_ip'] = TRUE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

$config['cookie_prefix']    = '';
$config['cookie_domain']    = '.jupiter.rjv.me';
$config['cookie_path']      = '/';
$config['cookie_secure']    = TRUE; // PS: tried FALSE version as well, but no change. 
$config['cookie_httponly'] = FALSE;

User.php controller

public function login_required() {
  if (!$this->logged_in()) {
    $this->session->set_flashdata("login_error", "You have to be logged in to see this page.");
    $this->session->set_userdata('redirect_back', $this->agent->referrer());
    redirectt('/login');
  }
}

routes.php

$route['login/required'] = 'user/login_required';

A simple method like this, when I browse to http://domain.ltd/login/required it redirects to http://domain.ltd/login with printing message like "You have to be logged in to see this page.". Once the user logins, it redirects user back to the page previously he/she was.

In my case it does redirect to /login page, but doesn't print out flashdata message.

Here is MY_Controller.php

class MY_Controller extends CI_Controller {
  protected $logged_in = NULL;
  protected $is_ajax   = NULL;
  protected $user_id   = NULL;

  public function __construct() {
    parent::__construct();

    log_message("DEBUG", "session variables: " . print_r($this->session->all_userdata(), true));

    $this->logged_in = $this->session->userdata('logged_in');
    $this->is_ajax = $this->input->is_ajax_request();
    $this->user_id = $this->session->userdata('user_id');
  }
}

As you see, I print out session variables on each request.

Here is the output of the sessions over HTTP request:

DEBUG - 2016-01-03 07:17:27 --> session variables: Array
(
    [__ci_last_regenerate] => 1451805447
)

Here is the output of the sessions over HTTPS request:

DEBUG - 2016-01-03 07:19:44 --> session variables: Array
(
    [__ci_last_regenerate] => 1451805564
    [redirect_back] => https://jupiter.rjv.me/book/1497-sefiller-viktor-mari-huqo
)

I haven't changed any code, just tried on both requests, HTTP and HTTPS. The session outputs are different. One doesn't save, the other does. I hope this would help you to identify the problem.

I was actually modifying headers on my .htaccess file and one rule was causing the issue. See the commented line - that line was the issue.

<IfModule mod_headers.c>
    Header append Vary User-Agent env=!dont-vary
    Header set X-XSS-Protection: "1; mode=block"
    Header unset Server
    Header set X-Content-Security-Policy "allow 'self';"
    # Header edit Set-Cookie ^(.*)$ $1;HttpOnly;Secure
</IfModule>