While a lambda is still processing (archive unpacking etc), the lambda state should be set to "Pending" (currently "Active") and invocations to that lambda should fail (currently, it can end up in a inconsistent state in this case, like lambdas being executed without layers).

Lambda state should reflect the current internal state, and invocations should fail if not active.
config = data.get("DeadLetterConfig")
        if not config:
            return
        self.dead_letter_config = config
        target_arn = config.get("TargetArn") or ""
        if ":sqs:" not in target_arn and ":sns:" not in target_arn:
            raise Exception(
                'Dead letter queue ARN "%s" requires a valid SQS queue or SNS topic' % target_arn
            )
    def get_function_event_invoke_config(self):