QGraphicsView cannot render video when there is a QWebEngineView - qt

Question

I am making a very simple application which plays a video using QMediaPlayer/QGraphicsVideoItem/QGraphicsScene/QGraphicsView and in the meantime, it displays a web page using QWebEngineView.
However, when the QWebEngineView shows, only the sound of the video is played. The widget shows only white. When QWebEngineView's ->show() is not called, the video plays normally.
I've tried QVideoWidget. It doesn't have such problem.
I'm thinking that the rendering of the QGraphicsView might have conflicts with QWebEngine's.
Here's the code:
#include "mainwindow.h"
#include <QApplication>
#include <QWebEngineView>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QMediaPlayer>
#include <QVideoWidget>
#include <QGraphicsVideoItem>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWebEngineView *webview = new QWebEngineView();
QMediaPlayer *player = new QMediaPlayer();
QGraphicsVideoItem *item = new QGraphicsVideoItem;
QVideoWidget *vwid = new QVideoWidget();
QGraphicsView *gview = new QGraphicsView();
player->setMedia(QUrl::fromLocalFile("/home/user/Videos/IMG_6201.MOV"));
//player->setVideoOutput(vwid);
player->setVideoOutput(item);
QGraphicsScene *gscene = new QGraphicsScene();
gview->setScene(gscene);
webview.setUrl(QUrl("https://www.google.com"));
gview->scene()->addItem(item);
//vwid->show();
player->play();
webview->show();
gview->show();
return a.exec();
}