After upgrading (by unpinning 3 Jupyter packages in my fork of docker-stacks) Jupyter Lab / Server no longer works (only Notebook is still OK).

To reproduce:

1. Clone my fork mirekphd/docker-stacks (or reproduce it by making this change).
2. build mirekphd/base-notebook container (cd base-notebook and docker build --tag mirekphd/base-notebook .)
3. Try to run Jupyter Lab:
   docker run -d --rm --name base-notebook -p 8989:8888 -e JUPYTER_ENABLE_LAB=1 mirekphd/base-notebook:latest && docker logs -f base-notebook
4. Navigate to localhost:8989 and see the "Unable to connect" browser error.
5. Switch to Notebook (e.g. -e JUPYTER_ENABLE_LAB_NOT) to see it works correctly.

Note that earlier today I raised a less reproducible (closed-source) version of this issue in jupyterlab/jupyterlab#9520, so you may find some additional hints / details there.