In dbo.ContactBase and dbo.ActivityPointerBase the same records are clearly being inserted multiple times long after the original record was created. We have noticed that the issue has gotten much worse since we recently enabled Server-Side Sync but the issue existed before that change. 

For example, a user may have created a contact in 2017, now in 2019 the contact is being "recreated" with new ContactIds but all displayed fields are identical and the Created By is the same 2017 user. In some cases the users may have gone on to a different department and no longer interact with CRM in any way, yet new Contacts are showing up "Created By" them.

We do use Kingswaysoft for some updates and inserts from SSIS and we are on-premise. I have not been able to find anything in the Kingswaysoft packages that would insert new records into these tables. On the duplicate contacts, it appears that dbo.ContactBase.VersionNumber is the only value changing between records. Please let me know what code I can provide to assist.