Submitting a form, when using the same form with different ID are on a page
You need to call your form like this:

$form = new Drupal\mypoll\Form\PollForm($nid);
$poll_form = \Drupal::formBuilder()-&gt;getForm($form);


Then add this methods to your form class:

protected $nid;

public function __construct($nid)
{
  $this-&gt;nid = $nid;
}

public function getFormId()
{
  return 'my_form-' . $this-&gt;nid;
}


And you need to make sure that $nid is different each time the form is on the page.