BuddyPress.org

Ok the problem is retroactive. Before recent versions, group wire posts were recording the wire_post_id as the primary ID in the activity stream, and not the group_id. This means the filter is picking up wire posts with the same ID as the new group.

There is really no way to fix this, it will not happen moving forward. Your best bet is to delete any activity that is not correct. It should be rare, and very limited – only one item in most cases.