CI 2.0.3 session heisenbug: the session is lost after some time 20 minutes, only when redirecting the server, there is nothing suspicious in the logs

It seems that I do not see any progress in this. My CI session settings are as follows:

$config['sess_cookie_name']     = 'ci_session';
$config['sess_expiration']      = 0;
$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'] = FALSE;
$config['sess_time_to_update']  = 7200;
$config['cookie_prefix']    = "";
$config['cookie_domain']    = "";
$config['cookie_path']      = "/";
$config['cookie_secure']    = FALSE;

The session library is loaded at startup. I commented on the sess_update function to prevent the AJAX error I found about reading the CI forum.

The table ci_sessionsin the database has sorting utf8_general_ci(there was an error that lost the session after each call redirect()and was due to the fact that the default was matching latin1_swedish_ci).

It always breaks after a user of my administration section tries to add a long article and clicks the save button. The save action is as follows:

function save($id = 0){
    if($this->my_model->save_article($id)){
        $this->session->set_flashdata('message', 'success!');
        redirect('admin/article_listing');
    }else{
        $this->session->set_flashdata('message', 'errors encountered');
        redirect('admin/article_add');
    }
}

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