I know this has been a documented issues for the past few years, but our troop has been recently experiencing this, where a scout will show up twice in the calendar event but there is only 1 account for that scout (I verified this). In this case the scout was a member of a different troop and the parent had merged the our troop with the former troop, so I wonder if this has anything to do with the bug?
If you have the Dynamic Meeting Invitations setting turned on under TroopTrack Settings - General Settings then it is something buggy if you do not have that setting turned on then this does happen. It seems to especially be with old events but can happen on new events as well. The fix is enabling the Dynamic Meeting Invitations.