*ngIf not working as expected with observable

Put the async pipe in parenthesis.

<a class="router-link nav-item" routerLink="/login" *ngIf="!(isLoggedIn$ | async)">
  Login
</a>
<a class="router-link nav-item" (click)="onLogout()" *ngIf="isLoggedIn$ | async">
  Logout
</a>