Symfony3 404 exception response return with status code 200 instead of 500

Question

I am new in symfony,I have facing one problem in Production Environment after I add kernel.event_subscriber in service.yml. problem is before adding event subscriber in service.yml file It return 500 HTTP_STATUS_CODE & Resource Not Found exception occur with my custom page in twingbuddle That I set, below page it show before add event_subscriber In Service.yml When I go to URL: http://localhost/meopin_2/trunk/web/en/login/ddssssssssss,

Then I add below code in Service.yml

kernel.event_subscriber:
class: AppBundle\EventSubscriber\TokenSubscriber
arguments: ["@security.http_utils","@service_container","@router", {}, {}, {},{}]
tags:
- { name: kernel.event_subscriber, channel: 'kernel' ,event: onKernelController,method: onKernelController}

and make a File Event Describer. Now issue is When I go to Same URL: http://localhost/meopin_2/trunk/web/en/login/ddssssssssss

It Return me Error as a Text Message with HTTP_STATUS_CODE 200, Below response It Return Me Instead of My Previous 404 Page in Production Environment.

What I missing or Wrong So that It return error as a text message in Production Environment ?

Thanks In Advance if Any one help me.