UITabBarController | | VC_Tab1 --------------------------- VC_Tab2 | | | | VC_Tab1_Child VC_Tab2_Child | (HeaderView) | (MyButton) The structure of the view controllers and views in the project is as described above. <case 1> self.navigationController?.popToRootViewController(animated: false) tabBarController.selectedIndex = 1 When popToRootViewController(animated: false) is called in VC_Tab1_Child, followed by setting the tab controller’s selectedIndex = 1, the following results are observed: viewWillAppear(_:), <VC_Tab2_Child> deinit, <VC_Tab1_Child> viewDidAppear(_:), <VC_Tab2_Child> The originally expected results are as follows viewWillDisappear(_:), <VC_Tab1_Child> viewDidDisappear(_:), <VC_Tab1_Child> deinit, <VC_Tab1_Child> deinit, <HeaderView> deinit, <MyButton> headerView.backButton.rx.tap -> Event completed headerView.backButton.rx.tap -> isDisposed viewWillAppear(_:), <VC_Tab2_Child> viewDidAppear(_:), <VC_Tab2_Child> The HeaderView belonging to VC_Tab1_Child was not deallocated, and the resources associated with that view were also not released. Similarly, VC_Tab1_Child.viewWillDisappear and VC_Tab1_Child.didDisappear were not called. <case 2> self.navigationController?.popToRootViewController(animated: false) DispatchQueue.main.async { tabBarController.selectedIndex = 1 } After performing the pop operation as shown in the code and waiting for a short period before testing, the expected results were generally achieved. (However, rarely, the results were similar to those observed when called without async.)” <case 3> self.navigationController?.popToRootViewController(animated: false) DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) { tabBarController.selectedIndex = 1 } When a sufficient delay was ensured as described above, the expected results were achieved 100% of the time.” The abnormal behavior is more pronounced in iOS versions prior to 18 and varies depending on the iOS version. I couldn’t find any documentation explaining the unexpected behavior shown in the results above. What could be the cause? The simulation code is provided below. https://github.com/linusix/UITabBarController_Test2