Vertex AI Integration Issue - Cannot read properties of undefined (reading 'Symbol(Symbol.asyncIterator)')

Google Cloud Build with AI AI Solutions
1

We are implementing Google Vertex AI (Gemini 2.5 Pro) inside n8n workflows, using the new AI Agent nodes and the Structured Output Parser to enforce JSON communication between agents.

Context

  • Workflow uses multiple AI Agents (Entry Agent → Stock Control → Finance → Marketing, etc.).

  • Each agent has its own prompt and JSON schema, processed through Structured Output Parser for consistency.

  • Vertex AI is connected via the native n8n Vertex AI node (not via HTTP Request).

Problem

  • On the very first AI Agent (Entry Agent), the workflow fails before parsing with the following error:
Problem in node ‘Agente de Entrada’
Cannot read properties of undefined (reading 'Symbol(Symbol.asyncIterator)')

  • This happens even when the JSON schema is valid inside the Structured Output Parser.

  • Yesterday the same workflow worked fine → today it fails with the error above, no schema changes.

  • It seems related to how the Vertex AI node returns its output to the Parser:

    • Sometimes the node returns undefined or non-iterable output.

    • The Parser then tries to iterate over undefined, triggering the error.

What we already tried

  1. Removed the Parser temporarily → workflow runs, so the issue is specifically on the Parser step.

  2. Checked the output of Vertex AI → sometimes plain text, sometimes malformed JSON.

  3. Tried Auto-Fix Format in the Parser → same issue.

  4. Updated Docker + n8n version → problem persists.

  5. Verified that in Vertex AI Console there is no saved prompt/schema (so output should be free-form).

Hypothesis

  • The error may be caused by the Vertex AI node using streaming output internally, while the Parser expects a fully resolved JSON object.

  • When the response is empty, malformed, or stream-based, the Parser receives undefined instead of iterable JSON.

Request

:backhand_index_pointing_right: Has anyone faced the Symbol.asyncIterator error when chaining Vertex AI → Structured Output Parser?
:backhand_index_pointing_right: Is there a known fix (e.g., disabling streaming, normalizing output with a Function node, or bugfix in recent n8n versions)?
:backhand_index_pointing_right: Should we switch to HTTP Request node + responseSchema instead of the native Vertex AI node for reliable JSON outputs?

2

Hi @eltonns74 ! :waving_hand: That error usually means the Vertex AI node is returning undefined or a stream, and the Parser can’t handle it. Try disabling streaming, or add a Function node to normalize the output before the Parser. If it keeps failing, using the HTTP Request node with a response schema is more reliable.