OSError: Unable to communicate with the jupyter_dash.., when using a custom env

Start by reproducing the reported call to JupyterDash.infer_jupyter_proxy_config() with a kernel from the custom environment. Trace the paths shown in jupyter_dash/jupyter_app.py and jupyter_dash/comms.py; done means the call no longer raises the reported communication OSError.

Running JupyterDash.infer_jupyter_proxy_config() throws an error, when using a kernel from the custom environment (not BBS-BBG). The following error is observed:

---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-5-44ad1f4b927e> in <module>
      1 time.sleep(3)
----> 2 JupyterDash.infer_jupyter_proxy_config()
      3 cyto.load_extra_layouts()

~/test-bbs-bbg-notebook/lib/python3.8/site-packages/jupyter_dash/jupyter_app.py in infer_jupyter_proxy_config(cls)
     71         else:
     72             # Assume classic notebook or JupyterLab
---> 73             _request_jupyter_config()
     74 
     75     def __init__(self, name=None, server_url=None, **kwargs):

~/test-bbs-bbg-notebook/lib/python3.8/site-packages/jupyter_dash/comms.py in _request_jupyter_config(timeout)
     60         if (time.time() - t0) > timeout:
     61             # give up
---> 62             raise EnvironmentError(
     63                 "Unable to communicate with the jupyter_dash notebook or JupyterLab \n"
     64                 "extension required to infer Jupyter configuration."

OSError: Unable to communicate with the jupyter_dash notebook or JupyterLab 
extension required to infer Jupyter configuration.