My first guess would be that the parent/scout are still invited to events in the pack. Most likely because:
- The events were set up with invitee lists prior to the scout being transferred and not cleaned-up afterwards, and/or
- The scout still has a membership active in the pack, and the parent/scout are continuing to get added to new events due to the scout’s appearance in the .
The parent can rule out 2 by checking the scout’s current memberships, and putting an end date on any that are in the pack. Issue 1 will require that the pack go through their events and “disinvite” the scouts/parents who are no longer with the unit. The Feature Assistant Extension can automate this, to some extent.
ETA: How did I miss that you’ve already checked for the residual membership? 
Sounds like it is most likely issue #1, then.
