Found in stress test: https://gist.github.com/alesapin/5cd6b8901488a1f170d5ef389900a534
Report: https://s3.amazonaws.com/clickhouse-test-reports/31158/7fb9a42b119b6c3eba1784caaabde51c1ded3384/stress_tests__debug__actions_.html
{
    auto & output = outputs.front();
    auto info = std::make_shared<ChunksToMerge>();
    info->bucket_num = bucket;
    info->is_overflows = is_overflows;
    info->chunks = std::make_unique<Chunks>(std::move(chunks));
    Chunk chunk;
    chunk.setChunkInfo(std::move(info));
    output.push(std::move(chunk));
}
bool GroupingAggregatedTransform::tryPushTwoLevelData()
{
    auto try_push_by_iter = [&](auto batch_it)
    {
        if (batch_it == chunks_map.end())
            return false;
        Chunks & cur_chunks = batch_it->second;
        if (cur_chunks.empty())
        {
            chunks_map.erase(batch_it);
            return false;
        }
        pushData(std::move(cur_chunks), batch_it->first, false);
        chunks_map.erase(batch_it);
        return true;
    };