Unset CDbHttpSession not working

I want to use database as session data storage (CDbHttpSession),
And I used this article too: slow-db-session-table
So I created YiiSession table in my db with this script:

CREATE TABLE `YiiSession` (

  `id` char(32) NOT NULL,

  `expire` int(11) unsigned DEFAULT NULL,

  `data` varchar(4096) DEFAULT NULL,

  PRIMARY KEY (`id`),

  KEY `expire_idx` (`expire`) USING BTREE


And after that, I changed the `main` config file like:

        'session' => [
            'class' => 'CDbHttpSession',
            'connectionID' => 'db',
            'sessionTableName' => 'YiiSession',
            'timeout' => 3600 * 24 * 30,
            'autoStart' => false,
            'autoCreateSessionTable' => false

But there are some issues,
1- When I add anything to my session first time it’s not set, and after second time it works.
2- My session doesn’t unset.


After unsetting my session, I print the session value and it’s NULL,but after refreshing page it’s still have the old value.

*Another thing is, after 2 more calling the method which changes the session value, it’s store the latest value of session.

What is the problem, Can anyone help me?