c++ - Getting error : Must construct a QGUIApplication first

Question

I am developing a GUI application, but whenever I am trying to close the application, it throws an error that "Must construct QGuiapplication first". My main is not returning exit code 0, so it's not exiting normally. I think some destructor is getting called twice but need some help here. I am attaching main.cpp code here for reference.

#include <QGuiApplication>
#include <QFontDatabase>
#include <QtWebEngine>

#include "ApplicationManager.h"
#include "AppLogger.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);

    QGuiApplication app(argc, argv);
    QtWebEngine::initialize();

    app.setApplicationName("MCS3.0");
    QFontDatabase::addApplicationFont(":/Fonts/Roboto.ttf");

#ifdef VERSION
    app.setApplicationVersion(QString("%1").arg(VERSION));
    logInfoMessage(app.applicationName()+app.applicationVersion()+" Started");
#endif

    ApplicationManager::instance().run();

    return app.exec();
}