Error when using `LANGCHAIN_TRACING` with concurrency

[spark-ming]

It appears that with this PR #381 , concurrency is supposed to be supported out-of-the-box. However, I get this error when setting LANGCHAIN_TRACING to true and then using the MapReduceDocumentsChain

TypeError: Cannot redefine property: __run
    at Function.defineProperty (<anonymous>)
    at StuffDocumentsChain.call (/backend/node_modules/langchain/dist/chains/base.cjs:64:16)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at MapReduceDocumentsChain._call (/backend/node_modules/langchain/dist/chains/combine_docs_chain.cjs:171:24)
    at MapReduceDocumentsChain.call (/backend/node_modules/langchain/dist/chains/base.cjs:53:28)
    at getAnswerFromDocs (/backend/src/nlp/qaChain.ts:34:18)
    at searchHandler (/backend/src/handlers/nlp.ts:19:20)

To replicate:

export const getAnswerFromDocs = async (question: string, docs: Document[]) => {
  const llm = new OpenAI(llmConfig);

  const qaChain = loadQAMapReduceChain(llm);

  const result = await qaChain.call({
    input_documents: docs,
    question,
  });

  return result.text;
};