Widgets not working in Jupyterlab 4

[swertz]

Hello,
First of all, thanks for this hugely useful tool!

I'm having some issues getting the widgets to work in jupyterlab 4.0.9. I have installed the packages ipywebrtc ipywidgets, and the extensions do appear in the jupyterlab extension manager:

However, creating an audio recorder does not work:

from ipywebrtc import AudioRecorder, CameraStream
camera = CameraStream(constraints={'audio': True,'video':False})
recorder = AudioRecorder(stream=camera)
recorder

Gives

[Open Browser Console for more detailed log - Double click to close this message]
Failed to load model class 'AudioRecorderModel' from module 'jupyter-webrtc'
loadClass@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/134.a63a8d293fb35a52dc25.js?v=a63a8d293fb35a52dc25:1:74936
loadModelClass@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/336.ebc7a55ea1768712771f.js?v=ebc7a55ea1768712771f:1:10729
_make_model@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/336.ebc7a55ea1768712771f.js?v=ebc7a55ea1768712771f:1:7517
new_model@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/336.ebc7a55ea1768712771f.js?v=ebc7a55ea1768712771f:1:5137
handle_comm_open@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/336.ebc7a55ea1768712771f.js?v=ebc7a55ea1768712771f:1:3894
134/v/this._handleCommOpen@http://localhost:8888/lab/extensions/@jupyter-widgets/jupyterlab-manager/static/134.a63a8d293fb35a52dc25.js?v=a63a8d293fb35a52dc25:1:73473
_handleCommOpen@http://localhost:8888/static/lab/jlab_core.60be43a866722f889a21.js?v=60be43a866722f889a21:1:1240940

When I open the same notebook with plain jupyter notebook (7.0.6), in the same environment, it does work fine: