WebEngine offscreen rendering does not work anymore after 5.12

I've made a forum post about this but unfortuately did not get any feedback: 

https://forum.qt.io/topic/112200/offscreen-rendering-does-not-work-with-qt-5-13-5-14

Basically what we're doing is creating a QWebEngineView and hide it by setting the attribute Qt::WA_DontShowOnScreen. 

We then use findChild<QQuickWidget *>() to get the widget with the OpenGL context and then we use glReadPixels to render the contents of the widget to a texture. 

I've held a talk about this at QtWS 2019: https://resources.qt.io/qt-world-summit-2019/modern-3d-user-interface-design-with-qt-quick-2

The problem now is that once we set WA_DontShowOnScreen the WebEngine will not update anymore. It will also not receive updates when the window containing the QWebEngineView is minimized.

So it seems that the WebEngine is only updated as long as the QWebEngineView is visble. It works up to Qt 5.12. (at least up to Qt 5.12.6). 

It doesn't work with any Qt 5.13 or 5.14 versions. The latest I tried is Qt 5.14.1. 

Until now I could not find any workaround to get offscreen updates back.