The progress bar does not show up, instead it is showing HBox(children=(FloatProgress(value=0.0, max=1.0), Label(value='In progress...')))
$ jupyter nbextension enable --py widgetsnbextension
# assuming you have already installed nodejs and jupyterlab
# otherwise you need to install nodejs and jupyterlab first (pip install jupyterlab)
$ jupyter labextension install @jupyter-widgets/jupyterlab-manager