Xcode 9 GM opening a storyboard crashes app on debug

Whenever I open Main.storyboard (without edting anything and without saving the storyboard) and then start debugging the app, the app immediately crashes. It looks like Xcode 9 modifies the storyboard even if only select it without changing anything. Re-starting Xcode does not help - the only thing that helps is restoring a backup of the whole project. Any expert with an idea? Thanks.


Stefan