JupyterHub 500: Server internal Error

In rare occasions you may this error when spawning a new JupyterLab instance or reconnecting to an existing one. In this case, you will need to manually cancel the failed instance and start a new one. 

You may go to the JupyterHub home at https://jupyterhub.ecmwf.int/hub/home and click on the red button "Stop My Server". After a few seconds, you will be able to start a new one with the desired settings.

JupyterHub error: n.map is not a function

This is a known bug that causes this random error when trying to open a new notebook from the launcher. The workaround is to use the left hand side file browser on the left hand side before. A simple click there, even on the white empty area in the file list, is enough to make it work.