JupyterLab has long launch delay. Caused by any extension? - jupyter

Question

My JupyterLab has a long launch delay. It takes ~ 20 seconds
from reading config json files
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.492 ServerApp] Paths used for configuration of jupyter_server_config:
to extension linkage
Jan 25 22:38:11 xinliupitt-prebuilt-20 bash[1625]: [I 2023-01-25 22:38:11.816 ServerApp] jupyterlab | extension was successfully linked.
Detailed logs are here:
Jan 25 22:37:41 xinliupitt-prebuilt-20 systemd[1]: Started Jupyter Notebook Service.
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.492 ServerApp] Paths used for configuration of jupyter_server_config:
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /etc/jupyter/jupyter_server_config.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.493 ServerApp] Paths used for configuration of jupyter_server_config:
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /usr/local/etc/jupyter/jupyter_server_config.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.493 ServerApp] Paths used for configuration of jupyter_server_config:
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/beatrix_jupyterlab.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/jupyter-server-proxy-jupyterserverexten>
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/jupyter_server_mathjax.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/jupyterlab.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/jupyterlab_git.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/jupytext.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/nbclassic.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/nbdime.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.d/notebook_shim.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /opt/conda/etc/jupyter/jupyter_server_config.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.619 ServerApp] Paths used for configuration of jupyter_server_config:
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /home/jupyter/.local/etc/jupyter/jupyter_server_config.json
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: [D 2023-01-25 22:37:53.619 ServerApp] Paths used for configuration of jupyter_server_config:
Jan 25 22:37:53 xinliupitt-prebuilt-20 bash[1625]: /home/jupyter/.jupyter/jupyter_server_config.json
Jan 25 22:38:07 xinliupitt-prebuilt-20 bash[1625]: Matplotlib is building the font cache; this may take a moment.
Jan 25 22:38:11 xinliupitt-prebuilt-20 bash[1625]: [I 2023-01-25 22:38:11.816 ServerApp] jupyterlab | extension was successfully linked.
Jan 25 22:38:11 xinliupitt-prebuilt-20 bash[1625]: [I 2023-01-25 22:38:11.816 ServerApp] jupyterlab_git | extension was successfully linked.
.
.
.
I tried to disable extensions one by one and see which one is the root cause of the delay. For example, I disabled extensions: "jupyter_server_mathjax", "jupyterlab", "jupyterlab_git", etc.
I can disable all extensions successfully (and found they are not root causes) except the "jupyterlab" extension. To disable "jupyterlab" extension, I tried these approaches
modify the content of jupyterlab.json from true to false
delete jupyterlab.json
before jupyter launch stage, use cmd jupyter labextension disable jupyterlab
try any of jupyter launch cmd below
jupyter lab --dev-mode # start JupyterLab in development mode, with no extensions
jupyter lab --core-mode # start JupyterLab in core mode, with no extensions
jupyter lab --app-dir=~/myjupyterlabapp # start JupyterLab with a particular set of extensions
However, none of them successfully disabled "jupyterlab" extension, since finally this log always appears
jupyterlab | extension was successfully linked.
I also tried if "buildCheck": false can disable the extensions.
page_config.json
jupyter_notebook_config.json
jupyter_config.json
No it didn't work; the log still shows "extension was successfully linked."
My questions:
Has anyone experienced JupyterLab long launch delay and how did you resolve it?
Is there any other approach for me to disable the "jupyterlab" extension?
Thanks a lot!