I am not sure, but think the problem is just an error what could be solved later on. So you could try it later if the problem is still there. The message say you could send in a feedback, which is as stated on the right. If you click on this button.
You will be able to define you problem and Mendix will check the issue. As can be seen below.
If this problem does not get solved after a few days you could also send an e-mail to email@example.com. The support desk will pick the problem and you will receive updates about your problem.
Hope this will solve your problem!
In this case there is nothing you can do but Mendix should be doing something. If you press the feedback button on the right side of your screen you give a notification to Mendix that something went wrong. I assume you clicked one of the lessons?
You can use the feedback button to report issues to Mendix.