Using QQmlApplicationEngine.load and QGuiApplication.exec to load a new screen

[rlush]

I have inherited some code that requires a reboot to load a new screen. When the device goes into a firmware upgrade mode they shut the whole system down, reboot the processor and start the application with a new command line switch. In an effort to speed things up without changing too much I want to call

qApp->exit( EXIT_CODE_FIRMWARE_UPGRADE_STATUS)

and then from main do something like this

    int iReturn = 0;

    do
    {
        if(iReturn == EXIT_CODE_FIRMWARE_UPGRADE_STATUS)
        {
            // Firmware Upgrade Mode
            engine.load ( QUrl ( QStringLiteral ( "qrc:/qml/FirmwareUpgradeStatus.qml" ) ) );
            qDebug ( ) << "Show firmware upgrade status from main";
        }
        else if(argv[1] == 0)
        {
            nvmFileHandler.removeUpgradedFirmwareVersion ( );
            engine.load ( QUrl ( QStringLiteral ( "qrc:/qml/main.qml" ) ) );
        }
        else if ( engine.rootObjects().isEmpty() )
        {
            qDebug ( ) << "Nothing was loaded into the engine, so exit";
            // Return something meaningful so we don't get stuck in a boot loop
            return -1;
        }

        // Start the Qt application based on what is loaded in the engine
        iReturn = app.exec( );

        // Unload whats there so we can load something new if needed
        engine.rootObjects().clear();

    }while(iReturn);

However, its telling me

EGLFS: OpenGL windows cannot be mixed with others.

Am I close to something useful or have I gone in the wrong direction? I don't want to have to rip all the old code up to do things the "right" way, I just need something better than reloading the entire program.