Use this query to find where users have their post migrated but they never followed the question to the target site.
Q&A about the site for members of the workforce navigating the professional setting
OwnerDisplayName, Posts.Id AS [Post Link]
PostHistory ON Posts.Id = PostHistory.PostId
PostHistory.PostHistoryTypeId = 36 AND
Posts.PostTypeId = 1 AND
OwnerUserId IS NULL
ORDER BY Posts.CreationDate DESC