title: [Angular 10][Rxjs] Why second pipe not firing
body: <p>I have two subscribers to the same Observable, but the second one not emitting values.
  Is there a limitation to pipe which I am lacking knowledge of?</p>
  <h3>component.ts</h3>
  <pre class="lang-js prettyprint-override"><code>  private readonly destroyed$ = new Subject&lt;void&gt;();
  
    public readonly vm$ = this.service.vm$.pipe(
      tap(console.log),
      takeUntil(this.destroyed$)
    );
  
    public readonly labels$ = this.service.vm$.pipe(
      zip(this.makeLabels),
      tap(console.log),
      takeUntil(this.destroyed$)
    )
  
    ...
    constructor(private readonly service: SomeService) {
      this.service.load();
    }
  
    ngOnDestroy(): void {
      this.destroyed$.next();
      this.destroyed$.complete();
    }
  </code></pre>
  <h3>some.service.ts</h3>
  <pre><code>  export class SomeService implements OnDestroy {
      private readonly destroyed$ = new Subject&lt;void&gt;();
      private _vm$ = new BehaviorSubject&lt;ViewModel&gt;(null);
      public readonly vm$ = this._vm$.asObservable().pipe(takeUntil(this.destroyed$));
      ...
      load() { this._vm$.next({...}) }
    }
  </code></pre>
  <h3>component.html</h3>
  <pre class="lang-html prettyprint-override"><code>&lt;ng-container *ngIf=&quot;vm$ | async as vm&quot;&gt;
    &lt;header&gt;
      &lt;pre *ngFor=&quot;let label of labels$ | async&quot;&gt;
         {{label | json}} 
      &lt;/pre&gt;
    &lt;/header&gt;
  &lt;/ng-container&gt;
  
  </code></pre>