How can I retake a challenge in Trailhead?  I thought I was able to this before.  I am in one of my Trailhead playgrounds.

Thanks,
Steve

On Trailhead:

https://trailhead.salesforce.com/modules/service_basics/units/service_basics_intro

Check Challenge button does not complete and returns message:

'Looks like we're having issues, please try again. If this issue persists, please contact us using the submit feedback section on the sidebar.'

Please advise

Hello in the "Create and Customize Lightning Apps" module. I have followed the instructions to setting up the Lightning App. However, "Home" despite being at the top does not show. Can anyone explain why this is?