Angular: How to correctly implement APP_INITIALIZER

I have a Angular 5.2.0 application. I looked up how to implement APP_INITIALIZER to load configuration information before the app starts. Here an extract of the app.module :

providers: [ ConfigurationService, < provide: APP_INITIALIZER, useFactory: (configService: ConfigurationService) =>() => configService.loadConfigurationData(), deps: [ConfigurationService], multi: true > ],

Here the configuration.service :

import < Injectable, Inject >from '@angular/core'; import < HttpClient >from '@angular/common/http'; import < Configuration >from './configuration'; @Injectable() export class ConfigurationService < private readonly configUrlPath: string = 'Home/Configuration'; private configData: Configuration; constructor( private http: HttpClient, @Inject('BASE_URL') private originUrl: string) < >loadConfigurationData() < this.http .get(`$$`) .subscribe(result => < this.configData = < test1ServiceUrl: result["test1ServiceUrl"], test2ServiceUrl: result["test2ServiceUrl"] >>); > get config(): Configuration < return this.configData; >>

Here is an example of a constructor of a component where the configData is used:

export class TestComponent < public test1ServiceUrl: string; constructor(public configService: ConfigurationService) < this.test1ServiceUrl = this.configService.config.test1ServiceUrl; >>

It works fine with all the components which are defined within the . But the same implementation in a component outside the does not work.
When I debug the respective constructor of the component where it does not work it says that configService is null .
Why is the APP_INITIALIZER executed before the constructor of a component inside the is called but not before the constructor of a component outside the ?