I have a user who when connects to outlook from the sharepoint calendar list causes the duplication of items existing in the list. There are no workflow running in the background that would be creating it. Also the issue is coming for only1 user creating events under his name. As soon as he disconnects the issue stops making me believe that the issue is with the outlook. He reinstalled the outlook but the issue still persists though. I read some blogs and they were blaming the same onrecurring items but in my case random evens are getting duplicated and none of them are recurring.