If an update that modifies a document's shard key is converted from a retryable write to a transaction, and that transaction errors, we intercept the error message as to avoid returning a transaction error to the client (which would be confusing as they issued a retryable write). In a recent refactor, we accidentally began unsetting the write error from the response after catching and rewriting the error, so we end up returning an ok status to the client rather than the rewritten error.