title: Angular 8 Mat-Autocomplete inside ngFor just showing on the last item
body: <br>
  I'm doing a custom form with a FormArray in Angular 8 and in every position i have an Autocomplete as an Input, but the behavior is not what i expected. It just shows up on the las position input.
  <p>Code:</p>
  <pre><code>&lt;div formArrayName=&quot;assignments&quot; *ngFor=&quot;let item of myForm.get('assignments')['controls']; let i = index;&quot;&gt;
      &lt;ng-container [formGroupName]=&quot;i&quot;&gt;
          &lt;div fxLayout=&quot;row&quot; fxLayout.lt-md=&quot;column&quot; fxLayoutGap=&quot;10px&quot;&gt;                       
             &lt;mat-form-field fxFlex=&quot;30&quot;&gt;
                  &lt;mat-label&gt;{{ 'product.providers.txt.provider' | translate}}&lt;/mat-label&gt;
                  &lt;input type=&quot;text&quot; matInput formControlName=&quot;id_provider&quot;[matAutocomplete]=&quot;providers&quot;&gt;
                  &lt;mat-autocomplete #providers=&quot;matAutocomplete&quot; [displayWith]=&quot;displayPv&quot;&gt;
                       &lt;mat-option *ngFor=&quot;let option of filteredOptions[i] | async&quot; [value]=&quot;option.id&quot;&gt;
                           {{option.provider_business_name}}
                       &lt;/mat-option&gt;
                   &lt;/mat-autocomplete&gt;
              &lt;/mat-form-field&gt;
          &lt;/div&gt;
       &lt;/ng-container&gt;
  &lt;/div&gt;
  </code></pre>
  <p>Here is an example:</p>
  <p><img src="https://i.stack.imgur.com/STRWz.png" alt="Text" /></p>