Session lost after form submit in wordpress

You have to call always session_start() for each request.

The mission of session_start() is:

• Creates a new session
• Restart an existing session

That means, if you have created a session, and you don't call to the method session_start(), the variable $_SESSION is not going to be fulfilled.

Except: If in your php.ini you have set the option session.auto_start to 1, then, in that case it is not needed to call the session_start() because the variable $_SESSION is fulfilled implicitly.

You need to move session start/resume into your Session's constructor.

Like so:

class session{    function __construct()    {        if (! session_id()) {            session_start();        }    }

Another thing to mention, every time you'll do new Session you'll be getting an object of the same functionality working with same global variable $_SESSION.

You don't need more than one $session object, it would be a good time to look into Singleton pattern.

You need to use wordpress global variable for condition that session is set or not something like :

global $session;if (!session_id()) {    session_start();}include get_template_directory() . "/custom/session.php";