The guest originally booked a stay that was 42 days long, so they got the monthly discount. The guest then requested a reservation alteration to change the start date by one day, which would result in a 41 day long reservation, which would still be over 28 days long so the monthly discount theoretically would still apply.
But when I saw the reservation alteration payout info, I saw that the guest would actually end up paying significantly more (nearly $500 more) for a reservation that was one day shorter. Why? Because in making the reservation alteration, the guest lost all applicable discounts, eg, they lost the monthly discount, and the new total cost was calculated at the normal nightly rate.
Is this intentional by Airbnb, that reservation alterations result in a loss of discount, or is this an error?