Haha that’s what I said!
It’s a Windows Phone 8.1
The issue is when tapping on the Menu button on mobile to bring up the list of pages. The image turns to an X but the menu doesn’t swing in from the left.
I just confirmed it is IE: just use an Internet explorer browser on a computer and reposition the screen to a mobile size, then try and hit the menu button, and you should see the problem.