HA stops very often

Since a last few days my HA stops very often. Now the last log entry is:
2019-02-07 15:54:30 ERROR (MainThread) [aiohttp.server] Unhandled exception
Traceback (most recent call last):
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/web_protocol.py”, line 447, in start
await resp.prepare(request)
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/web_response.py”, line 353, in prepare
return await self._start(request)
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/web_response.py”, line 667, in _start
return await super()._start(request)
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/web_response.py”, line 410, in _start
await writer.write_headers(status_line, headers)
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/http_writer.py”, line 112, in write_headers
self._write(buf)
File “/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/aiohttp/http_writer.py”, line 67, in _write
raise ConnectionResetError(‘Cannot write to closing transport’)
ConnectionResetError: Cannot write to closing transport

Any ideas?