Symfony2 : Failed to start the session because headers have already been sent

TL;DR Getting an error on a Linux box with Nginx / PHP-FPM stating "Failed to start the session because headers have already been sent.". Error is not occurring on Apache local machine setup

So on my local machine I have the Symfony2 app running fine. No errors are popping up. But as soon as I deploy to our Linux Server I'm getting this error when I call a certain Action within a Controller class

Failed to start the session because headers have already been sent. 

In the index action I have already called

$session = $this->getRequest()->getSession();

And in another action within the same controller class I'm calling it again. The error pops up when I try a

$session->set('foo', $bar);

In my Twig I'm calling the action by a form and a button with a formaction property like so

<form id='blahblah'>
    .... some fields here .....
    <button type='submit' formaction='{{path('2ndAction')}}'></a>
</form>

So on my local machine, running Apache everything run fine. The Linux server is using Nginx and php-fpm and it's crashing for some reason. I checked the phpInfo() and the session auto start is set to off. Not sure if this is an Nginx/php-fpm issue or not but I thought it may be pertinent information.

Here is the Controller declaration, indexAction(), and my 2ndAction()

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Session\Session;    
use CBSi\Utils\HTTPUtils\CURLUtil;

class StartController extends Controller
{
    /**
     * @var  CurlUtil $curlUtil
     */
    private $curlUtil;

    /**
     * @var Acces