ngIf doesn't evaluate the expression when it changes. Angular and Firebase

Question

First I set the isLoading property to "true" so the element isn't loaded yet.(this happens on AppComponent)

  export class AppComponent implements OnInit {
  isLoading = true;
  constructor(private authService: AuthService) {}
 .
 .
 .

bellow in the ngOnInit hook I have:

firebase.auth().onAuthStateChanged((user) => {
      if (user) {
        // User is signed in.
        this.authService.user = new User(user.displayName, user.email, user.photoURL, user.uid);

        console.log(user);
        this.isLoading = false;
        this.authService.isLogIn.next(true);
      } else {
        // No user is signed in.
        console.error('no user is login');
        this.authService.isLogIn.next(false);
      }
    });
    .
    .
    .

this code is an asynchronous one and I want that the user wait to check if him is login or not so I can change the header's UI. Besides I have another component that wraps the header. I call it inside the AppComponent with *ngIf=isLoading

The problem is that when the isLoading change its value to false I've never seen the AppHeader been rendered. So, why *ngIf doesn't evaluate that property again?

Here my AuthService:

import * as firebase from 'firebase';
// import {User} from "../../auth/models/user.model";
import {Router} from '@angular/router';
import { Injectable } from "@angular/core";
import {Subject} from "rxjs/Subject";
import {User} from "../../auth/models/user.model";

@Injectable()
export class AuthService {
  token: string;
  isLogIn = new Subject();
  user: User;
  constructor(private router: Router){}

  signinWithFacebook() {
    const provider = new firebase.auth.FacebookAuthProvider();
    provider.addScope('user_location');
    return firebase.auth().signInWithPopup(provider)
      .then(
        (res) => {
          console.log(res);
          this.getTokenId();
          localStorage.setItem('userInfo', JSON.stringify(firebase.auth().currentUser.providerData[0]));
          const userInfo = firebase.auth().currentUser.providerData[0];
          this.user = new User(userInfo.displayName, userInfo.email, userInfo.photoURL, userInfo.uid);

          this.isLogIn.next(true);
          this.router.navigate(['/dashboard']);
        }
      );
  }

  getTokenId() {
    firebase.auth().currentUser.getIdToken()
      .then(
        (tk) => {
          return this.token = tk;
        }
      );
  }

  logout() {
    return firebase.auth().signOut();
    // handle in component
  }

  getLocalUserInfo(): boolean {
    if(localStorage.getItem('userInfo')) {
      const transformStoredUser = JSON.parse(localStorage.getItem('userInfo'));
      this.user = new User(transformStoredUser.displayName, transformStoredUser.email, transformStoredUser.photoURL, transformStoredUser.uid);
      return true;
    } else {
      return false;
    }
  }
  isLogin():boolean {
    if (localStorage.getItem('userInfo')) {
      return true;
    }
    return false;
  }
}

AppHeader.ts

import { Component, OnInit } from '@angular/core';
import {AuthService} from '../../public/services/auth.service';
import * as  firebase from 'firebase';
import {User} from "../../auth/models/user.model";
import {Observable} from "rxjs/Observable";

@Component({
  selector: 'app-header',
  templateUrl: './header.component.html',
  styleUrls: ['./header.component.css']
})
export class HeaderComponent implements OnInit {
  isActivated = false;
  constructor(private authService: AuthService) { }
  ngOnInit() {
    this.authService.isLogIn.asObservable().subscribe(
      (data: boolean) => {
        this.isActivated = data;
      }
    );
    this.isActivated = this.authService.isLogin();
  }

}

AppHeader template


  MovieApp
  
  
    
      
        Inicio
      
      
        
      
      
        
          
            Ingresar
          
        
        
          
          
            
            
              Dropdown link
              Dropdown link
            
          
          
            Dashboard

ngIf doesn't evaluate the expression when it changes. Angular and Firebase

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