Proxy connection to remote jupyterlab stopped working

I have been using remote_jupyter_manager.py to start my jupyterlab on NESH for the past few months. Yesterday it suddenly stopped working, and I can't get to the bottom of it. Two days ago, it still worked and it is not clear to me what has changed in the meantime. I am currently in Lima and connect to NESH through the Geomar VPN. To sum up my problem:

connection to Geomar VPN -> works

ssh connection to NESH -> works

starting jupyter lab -> works

opening chrome -> works

loading jupyterlab -> fails (see attached image)

I am grateful for any suggestions!