Angular - app initializer not being called

I made several changes to an Angular 11 app and now there are a few things broken that I need to fix. What I don't understand is why the app initializer that I defined is not being called at all. The changes that I made shouldn't have impacted this, so I'd be grateful for some suggestions. I did it exactly as written in the official documentation:

function initApp(http: HttpBackend, settings: AppSettings): () => Observable<any> {
  console.log("INITIALIZING APP");
  var appInfoCall = () => new HttpClient(http).get<IApplicationInfo>(settings.appInfoApi).pipe(
  tap(data => {    
    console.log("APP INITIALIZATION COMPLETE");
    settings.appInfo = data;
  }));
  return appInfoCall; 
}

and the provider array in my app.module.ts:

...,
{
  provide: APP_INITIALIZER,
  useFactory: initApp,
  deps: [HttpBackend, HttpClient, AppSettings],
  multi: true
}
],
bootstrap: [AppComponent]

From the console output I can see that the initApp function isn't called at all. Any ideas why this is the case?

Since initApp is expected to be injected with two providers:

function initApp(http: HttpBackend, settings: AppSettings): () => {
  ...
}

Modify the APP_INITIALIZER provider (dep) as:

{
    provide: APP_INITIALIZER,
    useFactory: initApp,
    deps: [HttpBackend, AppSettings],
    multi: true,
}

Sample Demo on StackBlitz

Reference

APP_INITIALIZER (Usage note)