I'm experiencing this same thing and I'm not using the beta version. I'm using XCode 9.3 which is the latest non beta version.
I'm not using a UINavigationController, I have a UINavigationBar on it's own.
Anyways, I solved this by adjusting the top navigation bar constraint.
First you will need to create a property for the top bar constraint.
If you use interface builder you can simply drag the constraint onto your file and create an IBOutlet but if you use pure code you will need to add the property manually.
var topBarViewConstraint: NSLayoutConstraint?
// hide bar
topBarViewConstraint?.constant = -navigaitonBar.intrinsicContentSize.height
// unhide bar
topBarViewConstraint?.constant = 0
This is not ideal but it will get the job done.
You can even animate the constraints if you want.