Error 215 during Aggregation on Python Client

We encountered a problem when running map reduce on a large dataset with python client. The intention is to query on a secondary index then filter the records with a UDF to get an aggregate count on different status. When running on a small set with less than 2 million records, everything works. When the number of records returned by the secondary index exceeds 2 million, we encounter Error Code 215 (AS_PROTO_RESULT_FAIL_QUERY_DUPLICATE). We are unsure what this means in the context of the client.

We provide the codes we used to run the aggregation.

Python

def aggregate_rec(client, namespace, setname, as_ref_key):
    """Aggregates statistics for a given gallery
    :param client: aerospike client
    :param namespace: name of namespace holding records
    :param setname: gallery of records
    :param as_ref_key: gallery name
    :return:
    """
    if not client.is_connected():
        client.connect()

    # operation is idempotent, safe to retry
    query_policy = {
        'max_retries': 3,
        'sleep_between_retries': 2000,
        'total_timeout': 60000  # 60 seconds for query, default is 1s
    }

    # operation is idempotent, safe to retry
    apply_policy = {
        'max_retries': 3,
        'sleep_between_retries': 2000,
        'total_timeout': 60000  # 60 seconds for query, default is 1s
    }

    query = client.query(namespace, setname)
    query.select('a', 'b', 'rec_status', policy=query_policy)
    query.where(aerospike.predicates.equals('as_ref_key', as_ref_key))
    query.apply('v2_galleryQuery', 'aggregate_records', policy=apply_policy)
    subtotals = []

    def collect_subtotals(subtotal):
        subtotals.append(subtotal)

    def _aggregate_sumtotals(subtotals):
        totals = {'s1': 0, 's2': 0, 's3': 0, 'total': 0}
        if subtotals:
            for subtotal in subtotals:
                for k in subtotal.keys():
                    totals[k] += subtotal[k]
                    totals['total'] += subtotal[k]
        return totals

    query.foreach(collect_subtotals, policy=query_policy)
    return _aggregate_sumtotals(subtotals)

Lua script

function aggregate_records(stream)
    local function count(totalCount, rec)
        totalCount[rec['rec_status']] = totalCount[rec['rec_status']] + 1
        return totalCount
    end

    local agg_count = map();
    agg_count['s1'] = 0;
    agg_count['s2'] = 0;
    agg_count['s3'] = 0;
    return stream : aggregate(agg_count, count)
end

Client Version

Python Aerospike version 3.1.1

Server Version

7 :  edition
     Aerospike Enterprise Edition
8 :  version
     Aerospike Enterprise Edition build 4.2.0.5
9 :  build
     4.2.0.5
10 :  services
12 :  build_os
     ubuntu16.04

It seems like upgrading the python client to 3.4.0 fixes the issue.