langflow-ai/langflow · error · Error

Build job not found

Error message

Build job not found

What it means

Thrown by buildUtils when the GET request to stream events for a build job_id returns 404. The build job was created (the initial POST succeeded) but by the time the client subscribes to its event stream, the backend no longer knows the job.

Source

Thrown at src/frontend/src/utils/buildUtils.ts:407

        onBuildComplete,
        onBuildError,
        onGetOrderSuccess,
        onValidateNodes,
      };

      return performStreamingRequest({
        method: "GET",
        url: eventsUrl,
        onData: async (event) => {
          const type = event["event"];
          const data = event["data"];
          return onEvent(type, data, buildResults, eventCallbacks);
        },
        onDataBatch: (events) =>
          processBatchedEvents(events, buildResults, eventCallbacks, onEvent),
        onError: (statusCode) => {
          if (statusCode === 404) {
            throw new Error("Build job not found");
          }
          throw new Error("Error processing build events");
        },
        onNetworkError: (error: Error) => {
          if (error.name === "AbortError") {
            onBuildStopped && onBuildStopped();
            return;
          }
          onBuildError!("Error Building Component", [
            "Network error. Please check the connection to the server.",
          ]);
        },
        buildController,
      });
    } else {
      const callbacks = {
        onBuildStart,
        onBuildUpdate,

View on GitHub (pinned to 976ec789d2)

Solutions

1. Retry the whole build (new POST produces a fresh job_id) — usually succeeds after a transient restart
2. If running multiple backend replicas, enable sticky sessions or route build job endpoints to a single instance
3. Check backend restart/crash logs if the error repeats on every build
4. Avoid backgrounding/suspending the tab between starting a build and watching its events

try {
  await subscribeToBuildEvents(job_id);
} catch (e) {
  if (e instanceof Error && e.message === "Build job not found") {
    const { job_id: fresh } = await startBuildJob(postData); // full retry with a new job
    await subscribeToBuildEvents(fresh);
  } else throw e;
}

When it happens

Trigger: Subscribing to /build/{job_id}/events after the job expired (in-memory job registry cleared), the backend restarted between POST and GET, or multiple replicas behind a load balancer routed the events GET to an instance that never hosted the job.

Common situations: Backend restart or crash-loop during a build; horizontal scaling without sticky sessions for the events endpoint; long delay between build start and stream open (slow client, suspended tab).

Related errors

• Flow not found
• Error processing build events
• Error starting build process
• Error in streaming request.
• Job not found: {exc!s}

AI-assisted analysis of langflow-ai/langflow@976ec789d2 (2026-08-14). Data as JSON: /api/errors/47db1e9538fc9ea5. Report an issue: GitHub.