I posted an answer on StackOverflow:

See this issue: https://github.com/symfony/symfony/issues/6530 and this line: https://github.com/symfony/symfony/blob/2.4/src/Symfony/Compon...

It suggests to use BinaryFileResponse instead. Something like this:

$response = new Symfony\Component\HttpFoundation\BinaryFileResponse($file);
$response->setContentDisposition('inline');
$response->setTtl(300);
return $response;

//Or with setting the headers manually
return  new Symfony\Component\HttpFoundation\BinaryFileResponse($file, 200, $headers, true, 'inline');

//Or Laravel style:
return Response::download($file)->setTtl(300)->setContentDisposition('inline');
return Response::download($file, null, $headers)->setContentDisposition('inline');