Had the same issue and have not been able to leave reviews for 42 days.
Airbnb Support could only tell me that this is a global issue in response to a security issue. I can only assume this means hacking.
All that Airbnb Support can do is to tell me that the issue and my complaint is being escalated to the team dealing with this. However I have heard nothing back from said team.
The issue affects some hosts and guests who have being unable to review. This means the review functionality has been removed from the dashboard and its time to review email notifications have been removed.
My concern is how this will affect my Superhost status once the review functionality is restored.
A secondary concern is how quiet Airbnb is in acknowledging their issue and providing a solution.