remote harvester: WARNING Sending data failed. Exception Traceback (most recent call last)

[jayhohoho2019]

On some of my remote harvesters' debug.log, there are these messages:

2021-11-27T16:15:04.007 harvester chia.rpc.rpc_server : WARNING Sending data failed. Exception Traceback (most recent call last):
File "/home/ubuntu/chia-blockchain/chia/rpc/rpc_server.py", line 69, in _state_changed
await self.websocket.send_str(dict_to_json_str(payload))
File "/home/ubuntu/chia-blockchain/venv/lib/python3.8/site-packages/aiohttp/client_ws.py", line 150, in send_str
await self._writer.send(data, binary=False, compress=compress)
File "/home/ubuntu/chia-blockchain/venv/lib/python3.8/site-packages/aiohttp/http_websocket.py", line 687, in send
await self._send_frame(message, WSMsgType.TEXT, compress)
File "/home/ubuntu/chia-blockchain/venv/lib/python3.8/site-packages/aiohttp/http_websocket.py", line 656, in _send_frame
await self.protocol._drain_helper()
File "/home/ubuntu/chia-blockchain/venv/lib/python3.8/site-packages/aiohttp/base_protocol.py", line 84, in _drain_helper
assert waiter is None or waiter.cancelled()
AssertionError

On the farmer node, chia farm summary shows every harvester and the correct plot counts.
Remote harvesters are all Rpi4's. 8GB ram. swap is turned off. log level is WARNING. all on the same LAN

[iu2019]

Having the same exact issue. Would appreciate the clue for what could be the cause and the solution.