Session lost after redirect on Heroku (but no on localhost) [fixed]

Sorry, I did not noticed the last line of the config.php file: 

PHP Code:

$config['sess_save_path'] = sys_get_temp_dir(); 


However, I have just tried changing the session drive to database, and the session is still being lost.
So I think the issue is related to the ci_session cookie being changed each time that the page is reloaded.