Customer / user API no longer returning meta box json

Previously, we used the following code to retrieve JSON data from a user / WC customer via our custom rest route:

	$rest_controller = new WC_REST_Customers_Controller();
	$response = $rest_controller->prepare_item_for_response($user, $request);
	$response_data = $response->get_data();
	$response->set_data($response_data);
	return $response;

There's some more code but that's the basic bit. Until a few weeks (not sure how long) ago this returned our custom field group as a top-level item in the json. Something like what's shown below where field_group is the name of the field group and it contained all of the metabox data within that field group.

Now, we get nothing at all from the metabox data. We still get all the rest of the expected user/customer information. I suppose this could be a change in the WC_REST_Customers_Controller. But if you have made REST API changes, then perhaps this is related.

{... stuff ...
    "email": "[email protected]",
    "first_name": "Chris",
    "id": 110,
    "is_paying_customer": true,
    "field_group": [
         "person": { "name": "dave" },
        ... etc..
     ]
}

We do pay for a license (not sure what email it's under - could be this one).

Thanks.

Chris