"Error displaying widget" using Jupyter Lab 1.0.2

Possibly related to #124, I am trying to run a super simple example after following the installation instructions:

pip install ipympl

# If using JupyterLab
# Install nodejs: https://nodejs.org/en/download/
jupyter labextension install @jupyter-widgets/jupyterlab-manager
jupyter labextension install jupyter-matplotlib

nodejs info:

$ node -v
v10.16.0
$ npm version
{ npm: '6.9.0',
...
}

Jupyter info:

$ jupyter --version
jupyter core     : 4.5.0
jupyter-notebook : 6.0.0
qtconsole        : not installed
ipython          : 7.6.1
ipykernel        : 5.1.1
jupyter client   : 5.3.1
jupyter lab      : 1.0.2
nbconvert        : 5.5.0
ipywidgets       : 7.5.0
nbformat         : 4.4.0
traitlets        : 4.3.2

Simple example:

# Enabling the `widget` backend.
# This requires jupyter-matplotlib a.k.a. ipympl.
# ipympl can be install via pip or conda.
%matplotlib widget
# aka import ipympl
 
import matplotlib.pyplot as plt
 
plt.plot([0, 1, 2, 2])
plt.show()

Error:

Error displaying widget

Not sure what else I need, or where a version mismatch is, any help is appreciated. Thank you!

Inizia riproducendo l’esempio con le versioni indicate di ipympl, JupyterLab, Node.js e Jupyter e con i comandi labextension mostrati. Verifica la configurazione dell’estensione per i widget di JupyterLab e la compatibilità delle versioni; il lavoro è completato quando l’esempio visualizza il widget rappresentato invece di "Error displaying widget".