Use constructor objects (DI) of StatusBar and SplashScreen as shown below.

initializeApp() {
    this.platform.ready().then(() => {
      this.statusBar.styleDefault();
      this.splashScreen.hide();
    });
  }

Use the instances that Angular injects in the constructor (DI) instead of the static methods of the StatusBar and the SplashScreen classes, as shown below:

initializeApp() {
    this.platform.ready().then(() => {
        this.statusBar.styleDefault();
        this.splashScreen.hide();
    });
}