Tried it mutiple times in my trailhead sandbox and 2 dev sites (1 created last week and 1 created today).  This is in:

Prepare Your Salesforce Org for Users 
Create a Unique Account List View

  Newest error is:  

Step not yet complete in jen.xxxxxxxx@localflavor.som
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: RJCBNGZR

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