Unexpected Termination in n8n Flow with Multiple Loop Over Items Steps

Below are a few troubleshooting steps and things to verify when a long-running flow stops unexpectedly, especially when it involves iterating over many items:

1. Check Node Settings and Iteration Mode

• Verify that nodes in your loop aren’t set to “Execute Once” if you intend to process every item. Some nodes (or specific operations) are designed to run only once per execution, so double-check the settings in the node’s Settings tab.
• Make sure that if you’re using the Loop Over Items node, the Batch Size isn’t set too high for your system and that downstream nodes are configured to receive data in batches.

2. Isolate the Loop Section

• Try reducing the number of iterations (or items) temporarily to see if the flow completes successfully. This may help you determine if the issue is due to the number of items.
• Alternatively, break the workflow into smaller, manageable sub-flows. This can help pinpoint if a specific node or batch of iterations is causing the problem.

3. Check Logging and System Resources

• Look into your n8n logs for any warnings or resource-related messages. Even though endpoints return a 200 status, there might be underlying system-level issues (like memory or CPU limits) causing the process to terminate.
• Ensure that your system has enough resources to handle a large number of iterations. Heavy flows might run out of memory or hit other resource constraints even if n8n doesn’t output a specific error message.

4. Verify Workflow Connections

• Confirm that the connections between nodes are intact. The loop should correctly feed items from one node to the next. In some cases a misconfiguration in node connections can cause the flow to stop before reaching subsequent nodes.

5. Evaluate n8n Version and Upgrade Considerations

• Since you’re on version 1.55.3, review the changelog or community forums to see if there are any known issues with looping or large workflows in that release. In many cases, updating to a newer version can resolve such issues as performance or memory handling may have been improved.

Example: Using Loop Over Items with a Wait Node

As a best practice when processing large sets of data, consider batching your processing and adding a slight delay between batches. For instance:

JSONCopied
{
    "nodes": [
        {
            "parameters": {},
            "id": "node1",
            "name": "Manual Trigger",
            "type": "n8n-nodes-base.manualTrigger",
            "typeVersion": 1,
            "position": [250, 300]
        },
        {
            "parameters": {
                "batchSize": 100,
                "options": {}
            },
            "id": "node2",
            "name": "Loop Over Items",
            "type": "n8n-nodes-base.splitInBatches",
            "typeVersion": 3,
            "position": [450, 300]
        },
        {
            "parameters": {
                "unit": "seconds",
                "value": 1
            },
            "id": "node3",
            "name": "Wait",
            "type": "n8n-nodes-base.wait",
            "typeVersion": 1,
            "position": [650, 300]
        }
    ],
    "connections": {
        "Manual Trigger": {
            "main": [
                [{ "node": "Loop Over Items", "type": "main", "index": 0 }]
            ]
        },
        "Loop Over Items": {
            "main": [
                null,
                [{ "node": "Wait", "type": "main", "index": 0 }]
            ]
        },
        "Wait": {
            "main": [
                [{ "node": "Loop Over Items", "type": "main", "index": 0 }]
            ]
        }
    }
}

This pattern allows you to process items in batches while also giving the system a short break between iterations.

Conclusion

There isn’t a known looping bug specifically in n8n for version 1.55.3 that fits these exact symptoms, so the unexpected termination is likely due to configuration or resource constraints. Try the suggestions above and monitor your system logs closely. If the problem persists, consider updating n8n and engaging with the community forum (or raising an issue on GitHub) with your detailed workflow and logs.

Let me know if you need further assistance with any particular node configuration or additional troubleshooting details!