Stop "Unable to find fuzzy matched region in endpoint logs" in AWS C# sdk

Question

I'm running localstack along with my service in docker-compose:

  localstack:
    image: localstack/localstack:0.14.1
    ports:
      - "127.0.0.1:4510-4559:4510-4559"  # external service port range
      - "127.0.0.1:4566:4566"            # LocalStack Edge Proxy
    environment:
      - SERVICES=sns,sqs
      - DEBUG=${DEBUG-}
      - DATA_DIR=${DATA_DIR-}
      - LAMBDA_EXECUTOR=${LAMBDA_EXECUTOR-}
      - HOST_TMP_FOLDER=${TMPDIR:-/tmp/}localstack
      - DOCKER_HOST=unix:///var/run/docker.sock
    volumes:
      - "${TMPDIR:-/tmp}/localstack:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"

Everything works (I can use sqs in my app), but lots of logs like this are generated by my application:

Info|Amazon|Unable to find fuzzy matched region in endpoint localstack:4566
Info|Amazon|Unable to find exact matched region in endpoint localstack:4566

I am always passing region to my AwsClient like this:

      return new AmazonSimpleNotificationServiceClient(new ConnectionParameters()
      {
        Credentials = AwsCredentials,
        Region = AwsRegion
      });

Why AWS sdk is trying to discover endpoint, despite fact it's always explicitly configured? How I can force it to use provided region?