It is odd in many ways. As I understand it - a guest has made a reservation for your place but did not have the correct ID verification. Airbnb outs their request on hold while getting them to get their ID verification done. It is something like 12-24 hours. In the meantime, your calendar is blocked and there is no mail or notification sent to you explaining it, causing the confusion and worry that you and every other host experiences when seeing this anomoly. If they fill out everything correctly you will get a request as usual to accept or decline. If they don't it will just open those days. I don't use Instant Book so don't know if this is different in thta case but at least now you know.
Yes, and it isn't fair that the host loses potential bookings this way but thats the case!