WebEngine does not load page

In a case where a Web Application that is hosted by a webserver on localhost and is displayed by QWebEngineView, the webpage is not always loaded in certain cases. This error occurs more often the more load on the CPU is.

Even if the application is started with a simple HTML-page there was not a significant difference in the start-up behavior.

delay 0 msec: WEB-application does not start
delay 200 msec: WEB-application does not start
delay 500 msec: WEB-application starts in about 80%
delay 3000 msec: WEB-application starts almost, but also here failed sometime the start-up

It looks like the WEB-application is loaded too early and the QWebEngine is not ready to accept the WEB-application.

The QWebEngineView and the HTTP-server runs in the same EXE.
The MainWindow is visible but the content of the QWebEngineView is empty - see start_up.jpg.
After clicking "Reload" the QWebEngineView start loading the WEB-application.

On the next attempt starts the application correct and the QWebEngineView loads the WEB-application immediately. But a few attempts later failed the loading of the WEB-application again.

The only difference in the NOK attempt is, that the SLOT finishLoading will be not called.
Time traces for OK and NOK attempt are attached and also the whole debug output from Visual Studio.

The start-up sequence looks like follow:

create QApplication and show splash screen
QApplication()
QSplashScreen::show();

start HTTP server
QTcpServer::listen()

create and show QMainWindow
QMainWindow()
ui->setupUi(this);
connect(QWebEngineView, SIGNAL(loadFinished(bool)), SLOT(finishLoading(bool)));
QMainWindow::show()

start WEB socket server
QWebSocketServer::start();

start laoding HTML page (index.html)
QWebEngineView::load()

start main loop
QApplication::exec()

SLOT finishLoading:
QSplashScreen::finish();|

The patch https://codereview.qt-project.org/c/qt/qtwebengine/+/340965 did not help