In my app there is a "popup window" with Loader #1 that loads a qml with list of controls buttons, StackView and invisible Loader #2 that loads other qmls pages with different active policy and then depending on controls buttons put them in StackView - pretty similar to concept of ekke drawer_nav_x application https://appbus.wordpress.com/2016/06/20/drawer-navigation-app/ (by the way, thank you, Ekkehard
But when I could "close" popup window (set source of Loader #1 to "") fast enough after opening it, application get crash if transition animation of internal StackView is not finished yet.
It's not hard to get crash if set transition animation duration to several seconds. Sometimes app is not crashing by first attempt.
When closing Loader #1 its status is Loader.Ready.
Crash stack log attached.