title: ngx-chips: it's not possible to add a second tag from autocompleteItems
body: <p>I'm using <code>ngx-chips</code> with <code>autocompleteItems</code> for tags input, but after adding the first tag, the dropdown is not appearing anymore and also there is no error in the <code>console</code>.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;tag-input
      [ngModel]="columnsToIgnore"
      [ngModelOptions]="{standalone: true}"
      [placeholder]="'Enter variables to ignore'"
      [secondaryPlaceholder]="'Enter variables to ignore'"
      [onlyFromAutocomplete]="true"
      (onAdd)="addIgnoreColumn($event)"
      (onRemove)="removeIgnoreColumn($event)"
      theme='bootstrap'&gt;
       &lt;tag-input-dropdown
         [autocompleteItems]="selectedDataset.schema.columns"
         [displayBy]="'name'"
         [focusFirstElement]="true"&gt;
            &lt;ng-template let-item="item" let-index="index"&gt;
              {{ item.name }} : {{ item.type }}
            &lt;/ng-template&gt;
       &lt;/tag-input-dropdown&gt;
  &lt;/tag-input&gt;
  </code></pre>
  
  <p>when adding the first <code>tag</code>, the dropdown appears
  <a href="https://i.stack.imgur.com/OJCoJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OJCoJ.png" alt="enter image description here"></a></p>
  
  <p>but when trying to add a second one, the dropdown does not appear
  <a href="https://i.stack.imgur.com/fyxaF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fyxaF.png" alt="enter image description here"></a></p>
  
  <p><a href="https://stackblitz.com/edit/angular-feyu3j" rel="nofollow noreferrer">Stackblitz</a></p>