How to Fix 'async event loop error in production' in AutoGen (TypeScript)

If you’re seeing async event loop error in production with AutoGen TypeScript, you’re usually hitting a runtime mismatch: something in your app is trying to start, reuse, or nest an async execution context that the current process can’t safely handle. In practice, this shows up when AutoGen agents are called from serverless handlers, background jobs, test runners, or code that mixes promise chains and long-lived event loops.

The key point: this is rarely an “AutoGen bug.” It’s usually a lifecycle problem in your app around AssistantAgent, UserProxyAgent, or the runtime that drives them.

The Most Common Cause

The #1 cause is creating or reusing AutoGen agents inside a request handler while also starting multiple concurrent runs on the same loop/runtime.

A common failure pattern is:

• •instantiate agents per request
• •call run()/runStream() concurrently
• •reuse the same runtime or shared state across overlapping requests

That often produces errors like:

• •Error: event loop is already running
• •Error: Cannot run the event loop while another loop is running
• •UnhandledPromiseRejection: Error: async event loop error
• •TypeError: Cannot read properties of undefined (reading 'send') when lifecycle gets corrupted after a failed run

Broken vs fixed

// ❌ Broken: overlapping runs against shared state/runtime
import { AssistantAgent } from "@autogen/core";

const agent = new AssistantAgent({
  name: "support-agent",
  systemMessage: "You are a support assistant.",
});

export async function POST(req: Request) {
  const { message } = await req.json();

  // If two requests hit this at once, you can get loop/runtime conflicts
  const result = await agent.run([{ role: "user", content: message }]);

  return Response.json({ result });
}

// ✅ Fixed: isolate execution per request and avoid shared mutable runtime
import { AssistantAgent } from "@autogen/core";

export async function POST(req: Request) {
  const { message } = await req.json();

  const agent = new AssistantAgent({
    name: "support-agent",
    systemMessage: "You are a support assistant.",
  });

  const result = await agent.run([{ role: "user", content: message }]);

  return Response.json({ result });
}

If your workload is high-throughput, don’t just move the constructor. Put AutoGen work behind a job queue so only one worker owns the conversation state at a time.

Other Possible Causes

1) Calling AutoGen from an environment that doesn’t support long-lived async work

Serverless platforms and edge runtimes can kill or freeze the process before AutoGen finishes.

// Example problem area
export const runtime = "edge"; // often wrong for long-running agent workflows

Use a Node.js runtime instead:

export const runtime = "nodejs";

If you’re on AWS Lambda, make sure your timeout covers the full agent run and any tool calls.

2) Mixing await with unhandled background promises

If you kick off an AutoGen task and don’t await it, your handler may exit early while work is still running.

// ❌ Broken
agent.run([{ role: "user", content: "Draft an email" }]);
return Response.json({ ok: true });

// ✅ Fixed
const result = await agent.run([{ role: "user", content: "Draft an email" }]);
return Response.json({ ok: true, result });

This matters more when using tools, memory persistence, or multi-agent orchestration.

3) Re-entering the same agent flow recursively

A tool can call back into an agent run while the first run is still active. That creates nested execution and often triggers event-loop style failures.

// ❌ Tool calls back into same orchestration path
const tools = [{
  name: "lookupCustomer",
  execute: async () => {
    return await agent.run([{ role: "user", content: "Continue" }]);
  },
}];

Instead, keep tool execution side-effect free and return data to the current run:

// ✅ Tool returns data only
const tools = [{
  name: "lookupCustomer",
  execute: async () => {
    return { status: "ok", customerId: "C123" };
  },
}];

4) Version mismatch between AutoGen packages and Node.js

A bad package combination can surface as runtime errors that look like loop issues.

Check these:

{
  "dependencies": {
    "@autogen/core": "^0.x.x",
    "@autogen/agentchat": "^0.x.x"
  },
  "engines": {
    "node": ">=20"
  }
}

Common problems:

• •Node version too old for your AutoGen release
• •Mixed package versions across @autogen/*
• •ESM/CommonJS interop issues causing odd async failures

Run:

node -v
npm ls @autogen/core @autogen/agentchat

How to Debug It

1. •

   Check where the first failure happens

   • •Look for the earliest stack trace line involving AssistantAgent, UserProxyAgent, or your tool callback.
   • •The first error is usually real; later ones are fallout.
2. •

   Log request concurrency

   • •Add request IDs and log when each run starts/ends.
   • •If two runs overlap on one shared object, you found the issue.

console.log("run-start", requestId);
const result = await agent.run(messages);
console.log("run-end", requestId);

3. •

   Confirm runtime type

   • •Verify whether you’re on Node.js, edge, Lambda, Bun, or a test runner.
   • •If it works locally but fails in production, compare process model and timeout behavior first.
4. •

   Strip out tools and memory

   • •Run the simplest possible AssistantAgent flow.
   • •If it stops failing, add tools back one by one until it breaks again.

Prevention

• •Keep AutoGen execution isolated per request or per job. Don’t share mutable conversation state across concurrent handlers.
• •Use a queue/worker model for multi-step agent workflows instead of running them directly in HTTP handlers.
• •Pin compatible versions of Node.js and all @autogen/* packages in lockfile and CI.

If you want one rule to remember: don’t let two async conversations own the same AutoGen runtime at once. That’s what turns a normal production workload into an event-loop failure.

Keep learning

• •The complete AI Agents Roadmap — my full 8-step breakdown
• •Free: The AI Agent Starter Kit — PDF checklist + starter code
• •Work with me — I build AI for banks and insurance companies

By Cyprian Aarons, AI Consultant at Topiax.