May be a duplicate of https://github.com/localstack/localstack/issues/988 but due to the age I will re raise.

I'm having issues when I throw an exception in a lambda - it isn't appearing on my dead letter queue. Is there something I am missing, I would like an sqs event exception to appear on the poison queue when an exception happens.

Below is the basic config:
 ````
    sqsclient.create_queue(QueueName = 'test-queue')
    sqsclient.create_queue(QueueName = 'test-queue-poison')

    lambda_client.create_function(
            FunctionName='MyFunction',
            Runtime='dotnetcore2.1',
            Role='role',
            Handler='Handler',
            Code=code,
	    DeadLetterConfig={'TargetArn': 'test-queue-poison-arn'})

     lambda_client.create_event_source_mapping(
		EventSourceArn='test-queue-arn',
		FunctionName='MyFunction',
		Enabled=True,
		BatchSize=100,
		StartingPosition='LATEST')
````

So when I raise a new (.net)exception within the lambda function no message is going to the dead letter queue. I can confirm that all is attached together OK as all other scenarios work, and the above code is pseudo-ish.
"""
        Starts a repeating timer that triggers start_idle_container_destroyer_interval every 60 seconds.
        Thus checking for idle containers and destroying them.
        :return: None
        """
        self.idle_container_destroyer()
        threading.Timer(60.0, self.start_idle_container_destroyer_interval).start()
    def get_container_name(self, func_arn):
        """
        Given a function ARN, returns a valid docker container name.
        :param func_arn: The ARN of the lambda function.
        :return: A docker compatible name for the arn.
        """
        return 'localstack_lambda_' + re.sub(r'[^a-zA-Z0-9_.-]', '_', func_arn)
class LambdaExecutorSeparateContainers(LambdaExecutorContainers):
    def __init__(self):
        super(LambdaExecutorSeparateContainers, self).__init__()
        self.next_port = 1
        self.max_port = LAMBDA_API_UNIQUE_PORTS
        self.port_offset = LAMBDA_API_PORT_OFFSET
    def prepare_event(self, environment, event_body):