Missing neilime/php-css-lint library Error even after Ludwig Download

All that layout_builder_component_attributes_requirements() does is check if the CssLint\Linter class exists:

/**
 * Implements hook_requirements().
 */
function layout_builder_component_attributes_requirements($phase) {
  $requirements = [];

  if (!class_exists('CssLint\Linter')) {
    $requirements['lbca_php_css_lint']['title'] = t('Layout Builder Component Attributes');
    $requirements['lbca_php_css_lint']['description'] = t('The neilime/php-css-lint library is required. See README.md.');
    $requirements['lbca_php_css_lint']['severity'] = REQUIREMENT_ERROR;
  }

  return $requirements;
}

You've confirmed the package is correctly downloaded, so the Layout Builder Component Attributes module has done it's part with ludwig.json. It appears that Ludwig may be failing to register the project with the autoloader.

Have you tried clearing Drupal cache?