@sb I'm just starting with QML too so don't take anything i say as a good idea! but in the documentation it seems contentComponents width and height should be set to the parent Page width and height NOT BottomEdge.
I was still getting the same problems after changing this so I tried setting the contentComponent to a Rectangle and nesting the PageStack inside. After this, myStackPage.height no longer resets to 0.
Hope this might help