I am trying to login into a test sandbox, but I am getting a verification code request being sent to a random email address, therefore can't login. The admin login is the same. The person who created the sandbox has left the organization. How can I resolve?

I'm doing the simple lightning components challenge and have hit this problem in my existing trailhead org and a brand new dev org that I've just created:

Challenge not yet complete... here's what's wrong: 
There was an unexpected error while verifying this challenge. Usually this is due to some pre-existing configuration or code in the challenge Org. We recommend using a new Developer Edition (DE) to check this challenge. If you're using a new DE and seeing this error, please post to the developer forums and reference error id: QVWBQHAG