Airbnb released a fix for this issue, which should resolve the problem with missing reservation confirmation code in reviews and reservation alteration webhook notifications. They will continue to monitor this closely.

Airbnb continues to work on a fix for this issue.

Airbnb has identified an issue where reservation confirmation code is missing from the GET Reviews API as well as review webhooks. It started at approximately March 25 at 00:00 UTC. They are looking into the matter with urgency, and will post updates as soon as we have more information. https://airbnbapi.statuspage.io/incidents/gzm9b5tlfvhw