It sounds like there are blocks or settings on your Booking.com calendar that are pulling through to your Airbnb calendar. I would look for the problem on the Booking.com side, carefully checking all the calendar settings there. If it takes you a while to find the problem and if you are usually getting only a small number of bookings at a time, you can take the chance to unlink the calendars (and quickly manually enter any bookings) until you are able to figure it out.