by Mario Peshev on WordPress.org
Delete the Custom Fields from your postmeta table where assigned posts no longer exist.
Delete all Custom Field entries assigned to posts that do not exist in the posts table.
Navigate to Settings -> Remove Unused CFs and delete all postmeta for non-existing posts.
Backup your WordPress site files and database quickly and reliably.
Flex Fields is a WordPress plugin to add custom meta boxes for post types, pages, taxonomies, and more, using the flex_field() function.
Clean your WordPress! Eliminate unused and broken media files. For a faster, and better website.