Resolve and Prevent Duplicate Data in Salesforce Challenge will not complete

https://trailhead.salesforce.com/content/learn/modules/sales_admin_duplicate_management/sales_admin_duplicate_management_unit_2

Hi All - trying to complete this module. My rule is setup correctly as far as I can tell. I have saved and activated the rule, and waited until the email arrived in my inbox. The challenge will not complete. I have tried in one of my existing sandboxes, in another existing, and in a brand new box. None of them complete, with the error message simply reading "Challenge not yet complete in Playful Koala Playground

Whoops, looks like there was a problem. Please try again."

Has anyone completed this challenge recently? Anything you had to do that wasn't as presented in the challenge text?

Thanks!