I have started a new app a few days ago and began working with the simulator to test it. I started as an empty project and manually added the storyboard. The simulator build
In my case, it was a storyboard inside a framework for a Mac application. I was using:
let storyboard = NSStoryboard(name: "StoryboardName", bundle: nil)
and needed to use the framework's bundle identifier to get the correct bundle:
let storyboard = NSStoryboard(name: "StoryboardName",
bundle: Bundle(identifier: "com.company.FrameworkName"))