Issue #3306526 by SteffenR: Case mismatch between loaded and declared class names

src/Plugin/search_api/processor/DomainAccessIncludeAllAffiliatesProcessor.php

 <?php
 
-namespace Drupal\domain_access_search_api\plugin\search_api\processor;
+namespace Drupal\domain_access_search_api\Plugin\search_api\processor;
 
 use Drupal\domain\Entity\Domain;
 use Drupal\search_api\Processor\ProcessorPluginBase;