Why does the appStoreVersionLocalizations API return a 409 error for specific languages when making a PATCH request?

I am using the App Store Connect API to update app information.

When I send data for the Thai (th) locale, the update is successful. However, when I send data for English - United States (en-US), I receive a 409 error (STATE_ERROR).

Example Data (translations list)

✅ Success: th (Thai)

["th", "แอพซื้อขายหุ้นสาธิตนี้เป็นแอพที่ให้คุณฝึกซื้อขายหุ้นโดยไม่ต้องใช้เงินจริง", "เราได้ปรับปรุงฟังก์ชันการทำงานและแก้ไขข้อบกพร่องเพื่อให้ใช้งานได้สะดวกยิ่งขึ้น"]

❌ Failure (409 error): en-US (English - United States)

["en-US", "This stock demo trading app is an app that allows you to practice stock trading without using real money.", "We have enhanced functionality and fixed bugs to make it even more comfortable to use."]

Error Details The error occurs when executing the http.patch() request in the _updateAppStoreConnectInfo function.

Error log:

{
  "errors": [
    {
      "id": "899835a1-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
      "status": "409",
      "code": "STATE_ERROR",
      "title": "The request cannot be fulfilled because of the state of another resource.",
      "detail": "Attribute 'whatsNew' cannot be edited at this time"
    }
  ]
}

What I Have Tried

1. The request succeeds for th, but fails for en-US.
2. Both requests have the same format.
3. According to Apple’s official documentation (https://developer.apple.com/documentation) a 409 error occurs when there is an issue with the request data, but I am unsure what is incorrect.
4. I tested 32 languages, and some worked while others did not. In this inquiry, I picked th (Thai) and en-US (English - United States) as examples.

Questions

1. Why does the en-US request return a 409 error while the th request succeeds?
2. What could be causing the error message “Attribute ‘whatsNew’ cannot be edited at this time”?
3. Is there a way to resolve this issue?

Any help would be greatly appreciated. Thank you!