Hi @Jan Klimaszewski , Thanks for using Microsoft Q&A Platform.
Could you please open the developer console (F12 button) and capture the error messages/logs? If you can't connect to a notebook, make sure web socket communication isn't turned off/disabled. The troubleshooting documentation is available here. Additionally, I advise trying logging out and logging back into the ML studio. I would request you to try all of these and provide details so that we can better understand more about this.
You can also look for similar thread to see if they can help you.