Talking about a Rubic's Cube. You are viewing the charges in the 1st example from the guest's point of view. Why?, you are a host. The 2nd from host point of view, but that is subject of a new charge setup (the $15 charge for guests beyond 8).
May I suggest: Approach Airbnb (or post here) with the before and after of both timeline cases, BUT strictly from only a single point of view (host). It may be easier to follow. I think I know how they figure it out, but strange that in the 2nd case they are charging $11-12 per extra per guest which is odd IF your charge is suppose to be $15.