Comment 5 for bug 1477363

In your example, the Page is declared as an instance. When you close the application, the elements will be destroyed silently, without having their attached Component.onDestruction called.

When you use a Page declared in the way you reported in a PageStack or AdaptivePageLayout, the Page will not be destroyed by these components as it has not been created by the PageStack/AdaptivePagelayout. So you won't get the onDestruction triggered either. In order to have that coming, you need to declare your page as component and add that to the PageStack/AdaptivePageLayout, or in a separate QML document and use that.