Why are there two different JSON response structures returned by authorize.net

[dfswtest2]

I've observed that Authorize.net occasionally returns JSON responses with varying structures for transactions within the same environment. Specifically:

One Structure:
The transaction details are provided directly in a flat structure.
Example: 

{
    "accountType": "Visa",
    "accountNumber": "XXXX1111",
    "transId": "1200xxxxxxxx",
    "responseCode": "1",
    "authorization": "NILUxx",
    ...
}

Another Structure:
The transaction details are nested within a transactionData object, adding an additional layer to the JSON.
Example:

{
    "resultCode": "Ok",
    "messageCode": "Ok",
    "transactionData": {
        "accountType": "Visa",
        "accountNumber": "XXXX7671",
        "transId": "80777xxxxxx",
        "responseCode": "1",
        "authorization": "0960xx",
        ...
    }
}

This inconsistency occurs even when the same payment flow is used. This inconsistency is leading to confusion when handling the data,

Why does the response sometimes include a transactionData wrapper, while other times it’s available directly at the root level?