ios-branch-deep-linking-attribution: Callback on the initSession() function doesn't get called when app already installed

When I launch the app from a universal link on a device where the app is already installed, the callback on the initSession() function doesn’t get called. This is my AppDelegate code:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
    
    window = UIWindow(frame: UIScreen.main.bounds)
    
    func showHomeViewController() {
        
        //TODO: Remove for launch
        Branch.useTestBranchKey()

        Branch.getInstance().initSession(launchOptions: launchOptions) { (params, error) in
            
            guard error == nil, let parameters = params as? [String: AnyObject], let encodedReferralEvent = parameters[Branch.BranchKey.referralEvent.rawValue] as? NSString else {

                DispatchQueue.main.async {
                    self.setRootViewController(viewController: self.produceRootViewController(referralEvent: nil))
                }
                
                return
            }
            
            DispatchQueue.main.async {
                let referralEvent = API.Users.Get.MyDecodedInvitationObject(base64EncodedString: encodedReferralEvent as String)
                
                self.setRootViewController(viewController: self.produceRootViewController(referralEvent: referralEvent))
            }
        }
    }
    
    #if DEBUG
    if EnvironmentPickerViewController.shouldShowEnvironmentPicker() {
        let envPicker = EnvironmentPickerViewController.newInstance()
        envPicker.completion = showHomeViewController
        window?.rootViewController = envPicker
        window?.makeKeyAndVisible()
    } else {
        showHomeViewController()
    }
    
    #else

        showHomeViewController()
    
    #endif

    return true
}

func setRootViewController(viewController: UIViewController) {
    window?.rootViewController = viewController
    window?.makeKeyAndVisible()
}

func produceRootViewController(referralEvent: ReferralEvent?) -> RootViewController {
    let vc = ControllerFactory.newController(instantiator: .storyboard, configurator: RootConfigurator())
    var destinationDS = vc.router?.dataStore
    destinationDS?.referralEvent = referralEvent
    return vc
}

func application(_ app: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -> Bool {
    Branch.getInstance().application(app, open: url, options: options)
    return true
}

func application(_ application: UIApplication, continue userActivity: NSUserActivity, restorationHandler: @escaping ([Any]?) -> Void) -> Bool {
    // handler for Universal Links
    Branch.getInstance().continue(userActivity)
    return true
}

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    // handler for Push Notifications
    Branch.getInstance().handlePushNotification(userInfo)
}

When I launch the app after installing it from the App Store, the callback is called. Any ideas why there is this difference in behaviour?