This is a significant flaw in the system, and I have had this happen to me. A guest can request to book (or use IB) even if their profile is not complete, and it blocks your calendar but does not show up as a request. It’s confusing.
The guest may also be lacking connecting an internet verification, or other. In my case she had not connected her email, but her passport was verified.
It is very frustrating when they are to check-in that day and you don’t know if they will ever finish up their profile.
In my case I called airbnb. They tried to call the guest but the guest did not respond - so they cancelled the booking and my calendar opened up again. For all I know the guest got to a point in her verification process and thought ‘forget it’ and would never show up. Because the booking isn’t complete they don’t lose the money, but the host looses the opportunity to have a booking.
In my opinion, guests should not be able to block your calendar unless they have everything verified and ready to go. I have mentioned that to air. I hope they fix this!