Need hep with "tornado.iostream.StreamClosedError: Stream is closed"


I am getting this “tornado.iostream.StreamClosedError: Stream is closed” error from JupyerLab on couple of different browsers (Chrome and Safari). Sometimes it works after restart sometimes restart doesn’t help wither. Detailed error message below. Some 3-year old links suggest downgrading tornado version (6.X → 5.1.1) as a fix. Not sure if this is still worth a shot given my current version mix. Let me know if you have any tips.

notebook 6.2.0
jupyter-server 1.15.6
jupyterhub 1.3.0
jupyterlab 3.0.18

Task exception was never retrieved
future: <Task finished name=‘Task-256022’ coro=<WebSocketProtocol13.write_message..wrapper() done,
defined at /opt/conda/miniconda3/lib/python3.8/site-packages/tornado/> exception=WebSocket
Traceback (most recent call last):
File “/opt/conda/miniconda3/lib/python3.8/site-packages/tornado/”, line 1102, in wrapper
await fut
File “/opt/conda/miniconda3/lib/python3.8/asyncio/”, line 349, in __wakeup
tornado.iostream.StreamClosedError: Stream is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File “/opt/conda/miniconda3/lib/python3.8/asyncio/”, line 282, in __step
result = coro.throw(exc)
File “/opt/conda/miniconda3/lib/python3.8/site-packages/tornado/”, line 1104, in wrapper
raise WebSocketClosedError()