Background of ViewController disappears for a split second when dismissing a view controller on top of it

Question

I have attached a video demonstrating the issue. It is very subtle but it's very apparent. It happens on both a simulator and a real device but is more likely on a real device.

https://streamable.com/ejswnt

When I dismiss ViewController2, the pixels of the visual effect view of the welcomeVc at the very bottom disappears for a split second before reappearing.

Here is a minimum reproducible example. I hope I could get across the effect I am trying to go for.

class ViewControllerStack {

    static let shared = ViewControllerStack()
    
    var views: [UIViewController] = []
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        view = MKMapView()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        let welcomeVC = WelcomeViewController()
        welcomeVC.isModalInPresentation = true
        if let sheet = welcomeVC.sheetPresentationController {
            sheet.detents = [.custom(resolver: { context in
                return 200
            }), .medium()]
            sheet.prefersGrabberVisible = true
            sheet.preferredCornerRadius = 15
            sheet.largestUndimmedDetentIdentifier = .medium
        }
        
        present(welcomeVC, animated: true)
        ViewControllerStack.shared.views.append(welcomeVC)
    }
}

class WelcomeViewController: UIViewController {
    override func viewDidLoad() {
        let blurEffect = UIBlurEffect(style: .systemThinMaterial)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        blurEffectView.frame = view.bounds
        view.addSubview(blurEffectView)
        view.sendSubviewToBack(blurEffectView)
        
        let button = UIButton()
        button.setTitle("Go to View Controller 2", for: .normal)
        button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
        button.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(button)
        
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            button.widthAnchor.constraint(equalToConstant: 200),
            button.heightAnchor.constraint(equalToConstant: 44)
        ])
    }
    
    @objc func buttonTapped() {
        let vc2 = ViewController2()
        vc2.modalPresentationStyle = .overCurrentContext
        vc2.modalTransitionStyle = .coverVertical
        present(vc2, animated: true) {
            UIView.animate(withDuration: 0.75) {
                self.view.alpha = 0
            }
        }
        ViewControllerStack.shared.views.append(vc2)
    }
}

class ViewController2: UIViewController {
    override func viewDidLoad() {
        let blurEffect = UIBlurEffect(style: .systemThinMaterial)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        blurEffectView.frame = view.bounds
        view.addSubview(blurEffectView)
        view.sendSubviewToBack(blurEffectView)
        
        let button = UIButton()
        button.setTitle("Go back to Welcome VC", for: .normal)
        button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
        button.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(button)
        
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            button.widthAnchor.constraint(equalToConstant: 200),
            button.heightAnchor.constraint(equalToConstant: 44)
        ])
    }
    
    @objc func buttonTapped() {
        ViewControllerStack.shared.views.removeLast()
        guard let lastVCInStack = ViewControllerStack.shared.views.last else { return }
        lastVCInStack.dismiss(animated: true)
        lastVCInStack.view.alpha = 1
    }
}