Did you know that you can ask to clear cache when leaving #Fedilab?
Otherwise, you can do it manually with the app.
To German users of #TubeLab, the default instance for your country is https://peertube.at/, unfortunately this #Peertube instance is down. That's why you get an error.
You can pick up another instance that matches your expectations thanks to the instances picker. Look at media descriptions for details.
PS: We don't maintain this instance.