Drawing issues using SwiftUI view as a PrimaryView in uisplitviewcontroller - swift

Question

I am trying to use SwiftUI View as a primary view in a UISplitViewController.
I have setup and added my PrimaryViewController to the NavigationController in my SplitviewController, in Storyboard.
mySwiftUI view code is as follows:
struct Tile_SwiftUI: View {
var body: some View {
RoundedRectangle(cornerRadius: 15)
.fill( Color.red )
.frame(height: 100)
.padding()
}
}
And my PrimaryViewController setup is as follows:
import UIKit
import SwiftUI
class PrimaryViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let testVC = UIHostingController(rootView: Tile_SwiftUI() )
self.view.backgroundColor = UIColor.white
testVC.view.backgroundColor = UIColor.blue
addChild(testVC)
view.addSubview(testVC.view)
testVC.view.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
testVC.view.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor ),
testVC.view.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor ),
testVC.view.topAnchor.constraint(equalTo: view.topAnchor ),
testVC.view.bottomAnchor.constraint(equalTo: view.bottomAnchor ),
])
testVC.didMove(toParent: self)
}
}
It all works as expected on the iPhone and iPad landscape orientation, but on portrait orientation the primaryViewController gets an odd overlay. Please see attached images.
Here is also a link to the full project:
https://www.sticklets.co/code/SplitViewController_SwiftUI_bug.zip
Any ideas what is causing this?