Bug - Source Not Found

This problem occurs if the bookmark to which the cross-reference refers no longer exists.
This will be the case if you have deleted the text to which the cross-reference pointed.
When you delete content in Word, any bookmark within that content will be gone too.
The result is that any cross-reference that refers to a bookmark that no longer exists will no longer be able to show relevant content.
Instead, such fields will show the error text Error! Reference source not found.
The source in this case was the deleted bookmark range.