Actually, now that I look closer, SMF has the same session check, so you probably removed it to achieve that behaviour.
That's an option as well, in sources/controllers/BoardIndex.controller.php, close to the end of the page, there is:
public function action_collapse()
{
global $user_info, $context;
// Just in case, no need, no need.
$context['robot_no_index'] = true;
checkSession('request');
remove that last line:
checkSession('request');