会话在CI3中仍然过期

i'm using CI3 framework and apache 2.6 as web server.

for user login, i'm using session for keep user login data.

below session setting in config file;

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'usersessionx';
$config['sess_expiration'] = 0;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 0;
$config['sess_regenerate_destroy'] = FALSE;

like mention above, session_expiration was set to 0 which never expired.

the problem was, some of my user got session time out and when they click /navigate to another page, the will redirect to login page.

i was google around but never solve the issue.

any advice an suggestion are welcome.

thanks.

Your path value is set to NULL.

/*
|--------------------------------------------------------------------------
| Session Variables
|--------------------------------------------------------------------------
|
| 'sess_save_path'
|
|   The location to save sessions to, driver dependent.
|
|   For the 'files' driver, it's a path to a writable directory.
|   WARNING: Only absolute paths are supported!
|
|   For the 'database' driver, it's a table name.
|   Please read up the manual for the format with other session drivers.
|
|   IMPORTANT: You are REQUIRED to set a valid save path!
|
*/

Docs.