When you delete a Thing from your database, fields in other data types that referenced it may not be fully cleared. The field looks empty in your app, but the database still holds an orphaned reference to the deleted Thing.
What you might notice
Searches using an "is empty" condition return more results than expected
Repeating groups or database views filtered on empty fields include unexpected entries
Workaround
Run a bulk operation on the data type that contains the affected field. Set the affected field to empty for any items that still reference the deleted Thing. This clears the orphaned reference so future searches return accurate results.
For step-by-step guidance, see the Bulk operations article.
Status
We're aware of this behavior and are working on a long-term fix. The bulk operation workaround above should resolve the issue in the meantime.