If QWebengineView (via createWindowContainer)  and two QWidget are stacked in QStackedWidget and  when they are being switched using  QStackedWidget::setCurrentIndex(), the window will become blank during the process of hiding previously shown Web-engine view .

Attached is the example which reproduces this.

Steps to see the issue:
1. Click "QWebEngineView" in the toolbar: a QWidget involving a QWebEngineView is added to the QStackedWidget.
2. Click "Switch": a QWidget is added to the QStackedWidget
3. Repeat the previous two steps.
After the second step, you can see the view will become blank (or see a small green area) before it becomes green.

(Timer is added to make it more visible)

If you click  QWidgets and switch then it works fine.
1. Click "QWidget"
2. Click "Switch"