invalid instance of "Drupal\Core\Template\Attribute" for prop type="Drupal\Core\Template\Attribute"

Maybe it is because this logic:

    if (isset($definition['ui_patterns']['prop_type_adapter'])) {
      $prop_type_adapter_id = $definition['ui_patterns']['prop_type_adapter'];
      /** @var \Drupal\ui_patterns\PropTypeAdapterInterface $prop_type_adapter */
      $prop_type_adapter = $this->adaptersManager->createInstance($prop_type_adapter_id);
      $data = $prop_type_adapter->transform($data);
    }

is run by the ComponentElementBuilder instead of the ComponentElementAlter so is PropTypeAdapterInterface::transform() is executed before PropTypeInterface::normalize() instead of after.

Proposal: Move this logic to ComponentElementAlter, to be run after PropTypeInterface::normalize() .