I had the same problem and found an empty email address in the Profile | Settings page.
Entering an email address and agreeing to the terms meant I could continue my lessons. You have to agree if you want to continue learning. It's also the email address used to log into Azure for sandboxes. I tried using a different email address to that of my account but the sandbox and the in-browser cloudshell don't work.
On the plus side, at least you can 'Unsubscribe' afterwards which removes the email address (and resumes prevention of sandbox activation)