The following exception is raised unexpectedly on macOS versions 10.13, 10.12 & 10.11 at least. It appears to be macOS specific (works okay on Linux).

Further information can be found at the following links:
https://github.com/benoitc/gunicorn/issues/1487
http://erickt.github.io/blog/2014/11/19/adventures-in-debugging-a-potential-osx-kernel-bug/

[2017-03-20 00:46:39 +0100] [79068] [ERROR] Socket error processing request.
Traceback (most recent call last):
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/workers/async.py", line 66, in handle
    six.reraise(*sys.exc_info())
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/six.py", line 625, in reraise
    raise value
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/workers/async.py", line 56, in handle
    self.handle_request(listener_name, req, client, addr)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/workers/ggevent.py", line 152, in handle_request
    super(GeventWorker, self).handle_request(*args)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/workers/async.py", line 129, in handle_request
    six.reraise(*sys.exc_info())
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/six.py", line 625, in reraise
    raise value
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/workers/async.py", line 115, in handle_request
    resp.write(item)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/http/wsgi.py", line 362, in write
    util.write(self.sock, arg, self.chunked)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gunicorn-19.7.0-py3.6.egg/gunicorn/util.py", line 321, in write
    sock.sendall(data)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gevent-1.2.1-py3.6-macosx-10.12-x86_64.egg/gevent/_socket3.py", line 418, in sendall
    data_sent += self.send(data_memory[data_sent:], flags)
  File "/Users/ahmad/Projects/Side-Gigs/sa7beh-app/venv/lib/python3.6/site-packages/gevent-1.2.1-py3.6-macosx-10.12-x86_64.egg/gevent/_socket3.py", line 391, in send
    return _socket.socket.send(self._sock, data, flags)
OSError: [Errno 41] Protocol wrong type for socket