If you are using nginx as a webserver, it will try to buffer the response. So you'll want to disable this with a custom header:
.. code-block:: php header('X-Accel-Buffering: no'); # or with the Response class from Symfony $response->headers->set('X-Accel-Buffering', 'no');
Alternatively, you can tweak the `fastcgi cache parameters <https://nginx.org/en/docs/http/ngx_http_fastcgi_module.html#fastcgi_buffers>`_ within nginx config.
See `original issue <https://github.com/maennchen/ZipStream-PHP/issues/77>`_.