An Axure team member informed me that when viewing an Axshare prototype, if you make a very small change to the URL after you’ve hidden the top menu, you can refresh the page and you’ll get a new URL that completely displays without the top menu.
Original URL (with top menu hidden)
https://123456.axshare.com/#id=abcdef&p=title&c=1
Updated URL (change c=1 to c=2)
https://123456.axshare.com/#id=abcdef&p=title&c=2
Then refresh the updated URL
New URL is displayed (with no top menu)
https://123456.axshare.com/mypage.html