How to add an unique wrapper id to a widget element?

I made a widget that "generates" fields based on the option chosen of a select field. I got most of the logic done:

1- An option is chosen from this field:

 $element['value'] = [
  '#type' => 'select',
  '#options' => $this->getBreakpointsGroups(),
  '#default_value' => $value,
  '#ajax' => [
    'callback' => [$this,'updateBreakpoint'], // don't forget :: when calling a class method.
    'event' => 'change',
    'wrapper' => $wrapper_id, // This element is updated with this AJAX callback.
    'method' => 'html',
  ]
];  

2-Then the function updateBreakpoint is executed and it proceeds to update the form. First I extract the wrapper value in case there are multiple widget forms so it doesn't target another instance of the same form.

    $state = $form_state->getTriggeringElement();
    $wrapper_id = $state['#ajax']['wrapper'];

3- After making some changes to the form I return the changes and use an AJAX command

    $ajax_response = new AjaxResponse();
    $ajax_response->addCommand(new HtmlCommand("div#{$wrapper_id}",  $form['image_fieldset']));
    return $ajax_response;

The wrapper is defined inside the formElement function in the following way:

    $wrapper_id = Html::getUniqueId('wrapper');

The problem is that no change is made. When I define $wrapper_id as a string without any unique id functions ('wrapper' for example) the changes are made. I'm confused as to why. I made sure to check the value of the wrapper persisted in all the form.

If you have multiple wrappers on the same page you can't rely solely on Html::getUniqueId. You need to add as much predictable information as available.

For example in a single field widget element you can add the field name, the field parents and the field delta:

$field_name = $this->fieldDefinition->getName();
$parents = $form['#parents'];
$prefix = implode('-', array_merge($parents, [$field_name, $delta]));

$wrapper_id = $prefix . '-my-wrapper';