Codeigniter session expiring after an action

I made an administrative panel using CodeIgniter and every time the session expires, thus redirecting to the login screen. Every time, for example, that I edit a category, after editing it and clicking another menu link, the system redirects to the login screen again.

config.php (CodeIgniter default 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']    = FALSE;
$config['sess_table_name']      = 'ci_sessions';
$config['sess_match_ip']        = FALSE;
$config['sess_match_useragent'] = TRUE;
$config['sess_time_to_update']  = 300;

I do not know if these settings exist, since this "session expiration" is very fast.

The link menu link

user_model.php (login file)

<?php
class User_model extends CI_Model
{

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

    public function DadosUser()
    {
        $sessao = $this->session->userdata('user_id');

        if (!$sessao AND empty($sessao)) {
            redirect(base_url('login'));  
        } 

        $this->db->where('id', $sessao);
        $user = $this->db->get('admin_users');

        if ($user->num_rows() > 0) {
            return $user->row();
        }

        redirect(base_url('login'));
    }
}

categories_model.php (model responsible for category)

<?php
class Categorias_model extends CI_Model
{
    public function __construct()
    {
        parent::__construct();
    }

    public function NovaCategoria()
    {
        $config['upload_path'] = '../uploads/banners';
        $config['encrypt_name'] = true;
        $config['allowed_types'] = 'png|gif|bmp|jpg|jpeg|pjpeg';

        $categoria = $this->input->post('categoria');
        $ordem = $this->input->post('ordem');

        $query = $this->db->query("SELECT (MAX(codigo_categoria) + 1) AS codigo FROM Categorias");
        $novoCodigo = $query->row()->codigo;

        $data = array(
            'codigo_categoria' => $novoCodigo,
            'nome_categoria' => $categoria,
            'ordem' => $ordem
        );

        if (!empty($_FILES['userfile']['tmp_name'])) {

            $this->upload->initialize($config);

            if ($this->upload->do_upload()) {

                $upload = $this->upload->data();

                $data['imagem'] = $upload['file_name'];
            }
        }

        if ($this->db->insert('Categorias', $data)) {
            return '<div class="alert alert-success text-center">Categoria cadastrada com sucesso!</div>';
        }

        return '<div class="alert alert-danger text-center">Erro ao cadastrar categoria.</div>';
    }
}