Log flooded with unknown error 49.1

Does anyone understand what is causing below error and what I can do about it?

2017-08-04 21:11:59 ERROR (MainThread) [aiohttp.server] Unhandled exception
Traceback (most recent call last):
  File "/home/hass/.homeassistant/deps/aiohttp/web_protocol.py", line 435, in start
    yield from resp.write_eof()
  File "/home/hass/.homeassistant/deps/aiohttp/web_response.py", line 583, in write_eof
    yield from super().write_eof(body)
  File "/home/hass/.homeassistant/deps/aiohttp/web_response.py", line 420, in write_eof
    yield from self._payload_writer.write_eof(data)
  File "/home/hass/.homeassistant/deps/aiohttp/http_writer.py", line 282, in write_eof
    yield from self.drain(True)
  File "/home/hass/.homeassistant/deps/aiohttp/http_writer.py", line 295, in drain
    yield from self._stream.drain()
  File "/home/hass/.homeassistant/deps/aiohttp/http_writer.py", line 128, in drain
    yield from self._protocol._drain_helper()
  File "/usr/lib/python3.4/asyncio/streams.py", line 197, in _drain_helper
    yield from waiter
  File "/usr/lib/python3.4/asyncio/futures.py", line 388, in __iter__
    yield self  # This tells Task to wait for completion.
concurrent.futures._base.CancelledError