Unable to run JupyterLab interactive content - WebSocket error

I started following the course “Building Real-Time Video AI Applications” (Courses – NVIDIA), but, when running on Ubuntu 22.04, I’m not able to execute the cells of any notebook in the interactive environment. The python3 Kernel just does not connect, and by looking in the console (Google Chrome) I see a periodic error about WebSocket connection:

Also, I got a similar error by using the Firefox browser. In Windows, instead, everything goes fine. How can I solve this? Thanks in advance!