Situation:

• Airbnb Promo has been enabled for a property.
• The property receives three discounted bookings from Airbnb.
• One of the discounted bookings is cancelled.

Is the next booking for the property, which would be a fourth booking, going to have the 20% Promo discount?

Answer:
No.
Airbnb applies the 20% Promo discount to the next three bookings the property receives.
What happens after the booking has been received, is not taken into consideration by Airbnb.