When you embed a QQuickView using QWidget::createWindowContainer(), the QQuickView is blank in an external monitor when it is logically positioned to the left or on top of your primary display. In other words, when the whole widget is positioned into negative x- or y-coordinates.

The attached example demonstrates the problem. Toggle the button to show and hide the popup. In the primary display the popup is shown correctly (contains text QQuickView), in the secondary display (on the left side or on top of the primary display) the QQuickView is empty.

Also noticeable using a plain QRasterWindow.