I am getting the error under the Sales Reports for Lightning Experience - Extend Reports with Dashboards and Apps and my error code is: LKADQBCY    Please advise.

I've tried a second time using a brand new Trailhead Playground, and still get the error when checking the challenge:
"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: VRHJDGJD "

Once you complete a superbadge, you can no longer view the challenge list. Is there a list somewhere of all the superbadge challenges so I can go back and review them?