Why does my YCM Server shut down?

问题

Whenever I open vim, I get the message that Ycm Server has shutdown with exit code -6. The log files contain the following info:

2017-12-23 21:25:50,550 - ERROR - Unable to connect to server
Traceback (most recent call last):
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 217, in HandleServerException
    yield
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/youcompleteme.py", line 237, in CheckIfServerIsReady
    'ready' )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 68, in GetDataFromHandler
    timeout ) )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 183, in JsonFromFuture
    response = future.result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 404, in result
    return self.__get_result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 356, in __get_result
    raise self._exception
ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=54499): Max retries exceeded with url: /ready (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x10b7cbd50>: Failed to establish a new connection: [Errno 61] Connection refused',))
2017-12-23 21:25:50,655 - ERROR - The ycmd server SHUT DOWN (restart with ':YcmRestartServer'). Unexpected exit code -6. Type ':YcmToggleLogs ycmd_54499_stderr_MqYNI6.log' to check the logs.
2017-12-23 21:26:05,494 - ERROR - Unable to connect to server
Traceback (most recent call last):
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 217, in HandleServerException
    yield
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/shutdown_request.py", line 37, in Start
    self.PostDataToHandler( {}, 'shutdown', TIMEOUT_SECONDS )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 78, in PostDataToHandler
    timeout ) )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 183, in JsonFromFuture
    response = future.result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 404, in result
    return self.__get_result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 356, in __get_result
    raise self._exception
ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=54499): Max retries exceeded with url: /shutdown (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x10b80d2d0>: Failed to establish a new connection: [Errno 61] Connection refused',))
2017-12-23 21:26:05,618 - ERROR - Unable to connect to server
Traceback (most recent call last):
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 217, in HandleServerException
    yield
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/youcompleteme.py", line 237, in CheckIfServerIsReady
    'ready' )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 68, in GetDataFromHandler
    timeout ) )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 183, in JsonFromFuture
    response = future.result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 404, in result
    return self.__get_result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 356, in __get_result
    raise self._exception
ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=54502): Max retries exceeded with url: /ready (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x10b80d650>: Failed to establish a new connection: [Errno 61] Connection refused',))
2017-12-23 21:26:05,721 - ERROR - The ycmd server SHUT DOWN (restart with ':YcmRestartServer'). Unexpected exit code -6. Type ':YcmToggleLogs ycmd_54502_stderr_fNX8sk.log' to check the logs.
2017-12-23 21:26:14,523 - ERROR - Unable to connect to server
Traceback (most recent call last):
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 217, in HandleServerException
    yield
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/debug_info_request.py", line 41, in Start
    self._response = self.PostDataToHandler( request_data, 'debug_info' )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 78, in PostDataToHandler
    timeout ) )
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/autoload/../python/ycm/client/base_request.py", line 183, in JsonFromFuture
    response = future.result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 404, in result
    return self.__get_result()
  File "/Users/abhisheknaik/.vim/bundle/YouCompleteMe/third_party/pythonfutures/concurrent/futures/_base.py", line 356, in __get_result
    raise self._exception
ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=54502): Max retries exceeded with url: /debug_info (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x10b80da10>: Failed to establish a new connection: [Errno 61] Connection refused',))

Could someone please point out why is the connection lost? Running YcmRestartServer does not help as the server shuts down again.

Would highly appreciate any help. Thanks!