My understanding (which could be right or wrong, only going with my own experience as a host) is that the reviews only appear when both the host and guest complete the reviews.
So, it is possible that the hosts reviewed the guest but you don't see them as the guest did not complete theirs.
I understand why AirBnB keep them both private until both parties have completed them, as otherwise the second to complete would be privvy to the feedback on them first and that could influence how they construct their review.
But in your scenario it could be that a guest deliberately does not complete theirs, so the host review on them does not become visible.
I would ask AirBnB about it, but you could always remove that booking restriction that you have, as that is your choice.
Regards
Neil