Issue with Live Preview of UpFront Starter Themes

When clicking on the "Live Preview" for any of the UpFront Starter Themes (example, from this page: https://premium.wpmudev.org/project/scribe/) I get an "Authentication Required" popup. I've entered my login info for my premium account...tried a few times to ensure it wasn't user error :wink:...but every time it hangs, throws an error, or redirects to a page that mentions an invalid key. I'm able to login to my general account for premium.wpmudev.org

I'd love to use one of these themes but would like to take a look at the Live Preview first. Am I doing something wrong or missing a step?