Does the problem reproduce if you create a new test project?
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"
Seeing same problem on Sierra 10.12 using Xcode7.3.1 or Xcode8.0. Seem's to be Sierra related. If you restart your computer it seem's to work. When it fails it always seem's to fail at the same point. I've also noticed menus goes missing such as Search, just disappears, and you have to restart Xcode to get it back. Also New File Menu : Cocoa Touch Class has all messed up Menus.