Site Branding Block not appearing in regular page--html--twig template
You can probably override the suggestions using hook_theme_suggestions_page_alter in your THEMENAME.theme file

function THEMENAME_theme_suggestions_page_alter(array &amp;$suggestions, array $variables) {

  //the routes to use the specified template
  $use_template = [
    "user.register", // user/register
    "user.login", // user/login
    "user.pass", // user/password
    "entity.contact_form.canonical", // core contact form (website feedback)
    "entity.webform.canonical", // all webforms will have this route
  ];

  // what route are we on ?   
  $route_name = \Drupal::routeMatch()-&gt;getRouteName();

  if (in_array($route_name, $use_template) ){
    $suggestions[] = 'full__width__page';
  }
}


You should clear the cache and your specific template should take control.  

If you have twig debugging enabled and your browser has show html comments enabled you should see something similar to this the page source

&lt;!-- FILE NAME SUGGESTIONS:
   X full--width--page.html.twig
   * page--user--register.html.twig
   * page--user.html.twig
   * page.html.twig
--&gt;


With x indicating the twig template responsible for the particular output.  In this case full--width--page.html.twig is the twig template used.