We're in the process of tidying up some code to support the release of our Public API, which involves touching some of the implementation on our legacy API, which includes the legacy implementation of threaded post support. In this process we were making a change to the validation logic for threaded posts, which caused an issue during the thread creation process and resulted in this incident. This affected all users on our web platform who were trying to create threaded posts, non-threaded posts were not affected.

As we are in the process of migrating our clients to the new implementation of post creation on our GraphQL API, we will eventually reduce the risk from these incidents occurring (due to our new API having better infrastructure and testing setup). But in the meantime, we are adding improved review processes for code changes, along with better alerting to help us proactively catch these kind of issues.