WP会话在WP引擎托管上的AJAX功能中不可用

Question

I created a custom Wordpress plugin and it has a Ajax function in which I get data from the woocommerce session:

WC()->session;

Locally works perfect and I get the data from the session.

I am using WP Engine and installed the plugin on the live site and the session data in the ajax function is not available:

add_action( 'wp_ajax_test','test' );
add_action( 'wp_ajax_nopriv_test', 'test' );

function test() {
  var_dump( WC()->session );
}

But if I var_dump( WC()->session ) outside the ajax function everything is fine. So with their support we disabled the whole cache for testing but the problem stays the same.

Does anyone have any idea what might cause this strange behaviour on WP Engine server?