[Reg 5.15 -> 6.x] Re-initializing QGuiApplication causes QQmlApplicationEngine to crash

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main()
{
    for (int i = 1; i <= 3; ++i)
    {
        qDebug() << "Launching Qt app, repetition" << i;

        int argc = 1;
        QByteArray argv0("Window");
        QVector<char*> argv{argv0.data()};

        QGuiApplication app(argc, argv.data());
        QQmlApplicationEngine engine;

        qDebug("About to load main.qml...");
        engine.load(QUrl("qrc:/main.qml"));
        qDebug("...main.qml loaded");

        app.exec();
        qDebug("Window closed");
    }
}