QOpenGLWidget and QMacCocoaViewContainer do not work together

When a main window contains QWebEngineView and QMacCocoaViewContainer used for rendering VLC video, both the browser and the video seem to work at first. When sliding the splitter handle or resizing the window, QWebEngineView gets a black overlay and flickers heavily. Video disappears. This also happens, for example, when I go to my Chrome browser window while playing the video and then go back to my application - no video is shown anymore. 

I read that setting  QT_MAC_WANTS_LAYER environment variable may help in this case. On the contrary, in that case neither the browser nor the player show anything. Just a black background. The audio does play. The app crashes almost immediately.

[Update: code removed]

The project code and built packages for this sample with and without QT_MAC_WANTS_LAYER can be downloaded here: 

[Update: link removed as it is no longer available]

In case of using QOpenGLWidget instead of QWebEngineView behavior is different. 

[Update: code removed]

 There is a black square on the left, the sound works, but no video is playing. 

The code along with the compiled .dmg file can be found here:

[Update: link removed as it is no longer available]