scope and claims not working as expected

We ran in the same issue, following code should work with the current state on dev:

/**
 * Implements hook_oauth2_server_user_claims_alter().
 *
 * @param array $claims
 *   An array of claims.
 * @param \Drupal\user\UserInterface $account
 *   A user account object.
 * @param array $requested_scopes
 *   An array of requested scopes.
 */
function your_module_oauth2_server_user_claims_alter(array &$claims, \Drupal\user\UserInterface $account, array $requested_scopes) {
  if (in_array('openid', $requested_scopes)) {
    $claims['zipcode'] = $account->get('field_zip')->value;
    $claims['town'] = $account->get('field_city')->value;
    $claims['country'] = $account->get('field_country')->value;
    // etc.
  }
}

Nice, that does the trick. Thank you :-)