langflow-ai/langflow · error · Error

Flow not found

Error message

Flow not found

What it means

Thrown inside the streaming build path of buildUtils when the POST to the build-events endpoint returns HTTP 404. The frontend asked the backend to build/validate a flow by id and the backend has no flow with that id, so the stream is treated as 'Flow not found'.

Source

Thrown at src/frontend/src/utils/buildUtils.ts:313

        onBuildError,
        onGetOrderSuccess,
        onValidateNodes,
      };

      return performStreamingRequest({
        method: "POST",
        url: buildUrl,
        body: postData,
        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("Flow 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,
      });
    }
  } catch (e) {
    console.error(e);
  }

View on GitHub (pinned to 976ec789d2)

Solutions

1. Reload the page / refresh the flows list so stale flow ids are dropped from the store
2. Verify the flow still exists (GET /api/v1/flows/{id}) — a 404 confirms deletion or wrong id
3. If the DB was reset intentionally, restart the backend and reload the frontend so sessions realign
4. Recreate or re-import the flow if it was deleted

Example fix

// before: build against possibly-stale id
await runBuildEventsStream({ flow_id: flowIdFromStore });

// after: verify first, then build
const res = await fetch(`/api/v1/flows/${flowIdFromStore}`);
if (res.status === 404) {
  notifyAndReloadFlowList();
} else {
  await runBuildEventsStream({ flow_id: flowIdFromStore });
}

const res = await fetch(`/api/v1/flows/${flowId}`, { credentials: "include" });
if (!res.ok) { reloadFlowsAndNotify(); return; }

try {
  await streamBuildEvents(flowId);
} catch (e) {
  if (e instanceof Error && e.message === "Flow not found") {
    await refreshFlowStore(); // drop stale id, re-render list
  } else throw e;
}

When it happens

Trigger: Building a component in the canvas for a flow id that no longer exists in the DB: the flow was deleted in another tab/session, the database was reset, or the id in the URL/store is stale after a project/workspace switch.

Common situations: Long-lived browser tabs pointing at flows deleted elsewhere; DB wiped while the frontend kept cached flow ids; copying a flow URL with a truncated or wrong UUID.

Related errors

• Build job not found
• Error processing build events
• Error starting build process
• Job not found: {exc!s}
• Failed to load file (HTTP ${status})

AI-assisted analysis of langflow-ai/langflow@976ec789d2 (2026-08-14). Data as JSON: /api/errors/fe3f154cea1e3334. Report an issue: GitHub.