Reporting on Multi Person Event
|Knowledge Article Number||000006127|
|Description||A Multi-Person Calendar Event report displays each new invitee as a separate ID and the Assigned person is that invitee. So every new person added is a different Assigned person in your report.|
If you want to just see the person initially Assigned to the activity who is now an invited user. Then add this filter to your report:
"Event Invitation = False". If it's false it's the primary if not it's an invitee.