Starting a fullscreen QtQuick app by using showFullScreen() or setting this later by using setWindowState(Qt::WindowFullScreen) causes the view to no longer resize.

It neither resizes when the navigation and status bars disappear, nor when you rotate the screen. When you set the window state back to Qt::WindowMaximized, exiting the fullscreen, geometry update works again.

The QtQuickView's resize mode is set to QQuickView::SizeRootObjectToView.

This is a regression over 5.3 where this worked fine. I suspect the fix for the jumping during startup (QTBUG-38960) causes this or at least has a negative effect on this.