Failed to connect to server

At least in practice Vacuum Cleanner, console and gazebo failed to connect to server.

Do you have the latest RADI image? You can get it by running

docker pull jderobot/robotics-academy

Also, are you using the correct RADI launch instruction? There are some exercises that have slight differences. The one for Vacuum Cleaner is

docker run --rm -it -p 2303:2303 -p 1905:1905 -p 8765:8765 -p 6080:6080 -p 1108:1108 jderobot/robotics-academy python3.8

It’s also recommended to start a new container for each exercise you use. If you are on the terminal where the container is running you can stop it by pressing ctrl+c on Linux.

If none of the previous work for you, try cleaning the cache on your browser, there might be an update that is not loading.