Earlier today, we saw a spike in the number of posts that failed to publish to Facebook successfully. Posts were hitting "Unknown Error occurred" or "An unexpected error" occurred when attempting to publish via Facebook's API. This was due to a temporary issue in Facebook's API. This resulted in some posts from Buffer failing to publish to Facebook.
After monitoring this issue, we're confident things are resolved on Facebook's end. We are sorry for any trouble this was causing! Retrying any failed updates should see them published successfully.