Drawing issues using SwiftUI view as a PrimaryView in uisplitviewcontroller

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?