Bug Description

Initial discovery

I noticed this bug on a workflow that used to work. I take an array of messages from an email thread, and try to find the last one that fits a given condition. I used to do it with myArray.reverse().find( /* condition */) and it worked.

After an update to 2.20.9 this weekend we noticed this workflow had stopped working.

Clean reproduction

I setup a minimal reproduction for this bug, and it appears the bug is even deeper than expected. See the screenshot below :

As can be seen from the screenshot :

• The .reverse() unexpectedly mutated the result from the previous node in the UI
• $json.array.reverse() returns the correct result in the UI (reversed array) but null in the current node result
• As a result, findLast returns the last item from the reversed array in the UI, and the last item from the regular array in the current node result

Additionally i noticed that shuffling the order of the items in the Set node (such as swapping the positions of dataJsonReverse and dataJson) also unreverses some results and reverses others.

To Reproduce

• Create a Set node that assigns an array to a variable
• Create a subsequent Set node that returns :
  • the array from the previous node (untouched)
  • the array from the previous node (reversed)

The JSON for my reproduction case :

{
  "nodes": [
    {
      "parameters": {},
      "type": "n8n-nodes-base.manualTrigger",
      "typeVersion": 1,
      "position": [
        0,
        0
      ],
      "id": "6de26992-3164-45d4-b105-d1d7bcab454d",
      "name": "When clicking ‘Execute workflow’"
    },
    {
      "parameters": {
        "assignments": {
          "assignments": [
            {
              "id": "a4647ff5-30b9-4969-bb6e-affabeb14fdf",
              "name": "array",
              "value": "[1, 2, 3, \"four\"]",
              "type": "array"
            }
          ]
        },
        "options": {}
      },
      "type": "n8n-nodes-base.set",
      "typeVersion": 3.4,
      "position": [
        208,
        0
      ],
      "id": "30a6c738-7f64-4519-8063-ad9a741bdb43",
      "name": "Set initial array"
    },
    {
      "parameters": {
        "assignments": {
          "assignments": [
            {
              "id": "a3f714ed-56d3-4cab-81e3-e47566a02eec",
              "name": "dataJson",
              "value": "={{ $json.array }}",
              "type": "array"
            },
            {
              "id": "a0f2d256-b413-4e30-ab9f-4e2a723b4a00",
              "name": "dataJsonReverse",
              "value": "={{ $json.array.reverse() }}",
              "type": "array"
            },
            {
              "id": "67fe44e8-d6c2-4cb2-8141-ef548c74b741",
              "name": "dataJsonFindLast",
              "value": "={{ $json.array.findLast(a => a) }}",
              "type": "string"
            }
          ]
        },
        "options": {}
      },
      "type": "n8n-nodes-base.set",
      "typeVersion": 3.4,
      "position": [
        416,
        0
      ],
      "id": "8c9669a4-7810-4161-9d34-6244f8daf681",
      "name": "Edit Fields"
    }
  ],
  "connections": {
    "When clicking ‘Execute workflow’": {
      "main": [
        [
          {
            "node": "Set initial array",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Set initial array": {
      "main": [
        [
          {
            "node": "Edit Fields",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  },
  "pinData": {},
  "meta": {
    "instanceId": "fed5dc387fbe910582453b6033258970a80b35ec85ec315717e93873e0916584"
  }
}

Expected behavior

The reversed array should be returned correctly rather than returning null. Also the previous result should not be mutated.

Debug Info

Debug info

core

• n8nVersion: 2.20.9
• platform: docker (cloud)
• nodeJsVersion: 24.14.1
• nodeEnv: production
• database: sqlite
• executionMode: regular
• concurrency: 20
• license: enterprise (sandbox)
• consumerId: 00000000-0000-0000-0000-000000000000

storage

• success: all
• error: all
• progress: false
• manual: true
• binaryMode: filesystem

pruning

• enabled: true
• maxAge: 720 hours
• maxCount: 25000 executions

client

• userAgent: mozilla/5.0 (x11; linux x86_64) applewebkit/537.36 (khtml, like gecko) chrome/148.0.0.0 safari/537.36
• isTouchDevice: false

cluster

• instanceCount: 1
• versions: 2.20.9
• instances:
  • instanceKey: 71449d6f-3e60-4d38-bc0f-7196563c5000, hostId: main-felicity-dating-n8n-59d8d8b545-mc6j6, instanceType: main, instanceRole: leader, version: 2.20.9
• checks:
  • check: hostid-clash, status: succeeded, warnings: -
  • check: lifecycle, status: succeeded, warnings: -
  • check: split-brain, status: succeeded, warnings: -
  • check: version-mismatch, status: succeeded, warnings: -

Generated at: 2026-05-19T10:36:48.133Z

Operating System

N8N Cloud instance

n8n Version

2.20.9

Node.js Version

24.14.1

Database

SQLite (default)

Execution mode

main (default)

Hosting

n8n cloud