How do I display a modal dialog on page load, with working title and dialog options, using OpenModalDialogCommand? I'm trying to display a modal dialog containing some simple markup on page load. I'm getting the expected markup to load, and the dialog appears. However, the dialog title always displays &quot;Loading...&quot; and the options (width, specifically) don't appear to work.
I've got the following in my controller:
public function modal() {
  $config = \Drupal::config('popup.settings');
  $title = $this-&gt;t('Fnord');
  $content = [
    '#type' =&gt; 'processed_text',
    '#text' =&gt; $config-&gt;get('content')['value'],
    '#format' =&gt; $config-&gt;get('content')['format'],
  ];
  $options = [
    'dialogClass' =&gt; 'popup-dialog-class',
    'width' =&gt; '75%',
  ];
  $response = new AjaxResponse();
  $response-&gt;addCommand(new OpenModalDialogCommand($title, $content, $options));

  return $response;
}

...and the following javascript:
(function ($, Drupal, drupalSettings) {
  $(document).ready(function () {
    var ajaxSettings = {
      url: '/popup/modal'
    };
    var myAjaxObject = Drupal.ajax(ajaxSettings);
    myAjaxObject.execute();
  });
})(jQuery, Drupal, drupalSettings);

The result:

The width should be about 1152px on my screen, but is instead an even 600px; I assume that's a default, and that my $options array isn't overriding it as I would expect.
On the theory that this is only expected to work if the dialog is opened by a click event, I tried setting the dialog options in the javascript:
var ajaxSettings = {
  url: '/popup/modal',
  dialogType: 'modal',
  dialog: { width: 300 }
};

...however, the result was identical. What am I doing wrong?
It turns out the code above was working fine -- the problem was that the site was using a Bootstrap subtheme, and Bootstrap was configured to override the standard dialog behavior. Turning off Bootstrap's dialogs solved the problem, enabling both width and title settings.