title: Angular 9 - is not a known element
body: <p>It was working till angular 7 now after updating it it throws error of unknown elements. It's happening for shared modules.</p>
  
  <p>Reproducible Code: - <a href="https://stackblitz.com/edit/angular-ivy-pb3eea" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-ivy-pb3eea</a></p>
  
  <p>So I have a parent component 'Parent', 
  child component to be used inside router of 'Parent' - 'Child'
  a shared component to be used inside parent and child both - 'Shared'</p>
  
  <p>So I have imported in both modules of parent and child. (As using lazy modules), in parent it works but not in child.</p>
  
  <pre><code>import { NgModule } from '@angular/core';
  import { CommonModule } from '@angular/common';
  import { TestChildRoutingModule} from './test-child.routing.module';
  import { SharedModule } from '../shared/shared.module';
  
  @NgModule({
      declarations: [
      ],
      imports: [
          CommonModule,
          SharedModule,
          TestChildRoutingModule
      ],
      exports: [
      ]
  })
  export class TestChildModule { }
  
  </code></pre>