This is my case:
let passwordSecureTextField = app.secureTextFields["password"]
passwordSecureTextField.typeText("wrong_password") //here is an error
UI Testing Failure - Neither element nor any descendant has keyboard focus. Element:
This issue caused me a world of pain, but I've managed to figure out a proper solution. In the Simulator, make sure 'Hardware -> Keyboard -> Connect hardware keyboard' is off.