Zend certified PHP/Magento developer

2 errors Could not acquire lock for index: when reindexing

When I reindex a Magento 2.4.4-p2 webshop, I’m getting the following errors:

Category Products index process error during indexation process:
Could not acquire lock for index: catalog_category_product
Product Categories index process error during indexation process:
Could not acquire lock for index: catalog_product_category
  • I have reset the indexes
  • I checked the file permissions
  • There are no hanging cron jobs

Anyone have an idea what causes this problem and how to fix it?