This flakiness just caused a PR merge to be blocked by AppVeyor for me:

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ERROR: test_with_statement (test.test_nntplib.NetworkedNNTP_SSLTests)
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Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_nntplib.py", line 242, in wrapped
    meth(self)
  File "C:\projects\cpython\lib\test\test_nntplib.py", line 264, in test_with_statement
    with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
  File "C:\projects\cpython\lib\nntplib.py", line 1077, in __init__
    self.sock = _encrypt_on(self.sock, ssl_context, host)
  File "C:\projects\cpython\lib\nntplib.py", line 292, in _encrypt_on
    return context.wrap_socket(sock, server_hostname=hostname)
  File "C:\projects\cpython\lib\ssl.py", line 405, in wrap_socket
    return self.sslsocket_class._create(
  File "C:\projects\cpython\lib\ssl.py", line 853, in _create
    self.do_handshake()
  File "C:\projects\cpython\lib\ssl.py", line 1117, in do_handshake
    self._sslobj.do_handshake()
OSError: [Errno 0] Error
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https://ci.appveyor.com/project/python/cpython/builds/21299396

I lucked out by kicking it with a no-op change to re-trigger an appveyor run where it passed.