Running the attached sample code gives a warning of a failed Q_ASSERT at line 217. The point with id of 0 is not released properly when QQuickOverlay 'overlay', as the child of QQuickWindow 'window', also has its own child, i.e., QQuickItem. If the QQuickItem is commented, the program runs just fine. 

According to customer, the issue is:

'The cleanup code which runs setExclusiveGrabber(nullptr) found in "bool QQuickWindow::event(QEvent *event)" is never run. This is because the overlay uses an event filter on the QQuickWindow when it has a child and runs its own flawed version of event handling, which does not do the same cleanup.'