angular.getTestability(angular.element('body')).whenStable - takes too long time

Can any one give some good reasons why

 angular.getTestability(angular.element('body')).whenStable(function () {
                        console.log("angular is stable")
                    })

takes about a minute to be stable, while the page already loaded fully, no more network or something else. It just takes too much time.

The app is bootstraping with angular2 upgrade:

platformBrowserDynamic().bootstrapModule(AppModule).then(platformRef => {
    const upgrade = platformRef.injector.get(UpgradeModule) as UpgradeModule;
    upgrade.bootstrap(document.body, ['myApp']);
});