I'm not sure yet if this is happening to the user emails that are sent (order completion) but after upgrading to 6.84, not all but most admin emails are being sent as duplicates.  This started specifically at Smith Cart 6.84 upgrade.  I have an order that went through about an hour before upgrading and another right after.   The one right after upgrade was the first time I've seen this and it continues to happen on most (not all - probably 95-99%) of the orders. 

It seems to be the email triggered as the admin email template sent at order completion.  I'm on DNN 7.3.4 and as I said before Smith Cart 6.84

Sorry it took me a bit to gather this up. No third party cc and email manufacturers is turned off. Its doing it on a brand new instance that is setup with only one email selected.