channels: Daphne freezes on some ws disconnects

python 3.8
channels==2.3.1
channels-redis==2.4.1
daphne==2.4.0
Django==2.2.8

Entrypoint is daphne on alpine linux.
Consumer is quite simple:

class Consumer(AsyncWebsocketConsumer):
    async def connect(self):
        self.user = self.scope["user"]
        self.name = self.scope["url_route"]["kwargs"]["name"]
        # this line is changed by different subclasses
        self.group_name = "%s%s" % ("chat-", self.name)

        await self.accept()
        # Join group
        await self.channel_layer.group_add(self.group_name, self.channel_name)

        if not True: # auth check
            await self.send(text_data="not authorized")
            await self.close()

    # Receive message from group
    async def m(self, event):
        message = event["m"]

        # Send message to WebSocket
        await self.send(text_data=json.dumps(message))

This is the error that comes up after a random amount of disconnects:

2019-12-15 15:57:32,107 WARNING  Application instance <Task pending name='Task-21465' coro=<SessionMiddlewareInstance.__call__() running at /usr/local/lib/python3.8/site-packages/channels/sessions.py:178> wait_for=<Future pending cb=[_chain_future.<locals>._call_check_cancel() at /usr/local/lib/python3.8/asyncio/futures.py:357, <TaskWakeupMethWrapper object at 0x7f7ebec32910>()]>> for connection <WebSocketProtocol client=['127.0.0.1', 41380] path=b'/api/ws/chat/ddd8ce11-50d0-456a-b8d8-15a068682d1e/'> took too long to shut down and was killed.
2019-12-15 15:57:33,108 ERROR    Exception in callback AsyncioSelectorReactor.callLater.<locals>.run() at /usr/local/lib/python3.8/site-packages/twisted/internet/asyncioreactor.py:287
handle: <TimerHandle when=1090864.949068441 AsyncioSelectorReactor.callLater.<locals>.run() at /usr/local/lib/python3.8/site-packages/twisted/internet/asyncioreactor.py:287>
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/asyncio/events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "/usr/local/lib/python3.8/site-packages/twisted/internet/asyncioreactor.py", line 290, in run
    f(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/daphne/server.py", line 275, in application_checker
    exception = application_instance.exception()
asyncio.exceptions.CancelledError

Subsequent requests, http and ws, aren’t served anymore. Timeout.

Any insight into this at all is greatly appreciated!