Submitted data not returning data from conditional fields

I have my form set up like this:

[select* topic include_blank "Test1|[email protected]" "Test2|[email protected]" "Test3|[email protected]"]

[group group_topic_test1 clear_on_hide]
  [select* topic_test1 include_blank "AMG" "PRG" "KGL"]
[/group]

[group group_topic_test2 clear_on_hide]
  [select* topic_test2 include_blank "ORG" "COB" "MNM"]
[/group]

[group group_topic_test3 clear_on_hide]
  [select* topic_test3 include_blank "IRS" "LOM" "NJH"]
[/group]

When the first topic is selected, I get the first group of dropdown displayed and so on. This is all working fine.

However in the functions.php file, the submitted data $data = $submission->get_posted_data() is not returning the data from the group fields:

function action_wpcf7_before_send_mail_test( $contact_form ) {
    $form_id = $contact_form->id();

    if ($form_id == "234") {
        $submission = WPCF7_Submission::get_instance();

        if ($submission) {
            $data = $submission->get_posted_data();
        }
    }
    .........
    .........
    .........
    .........
}

It returns the selected ‘topic’ but not the group data:

$data: Array
(
    [topic_test1] => Array
        (
            [0] => 
        )

    [topic_test2] => Array
        (
            [0] => Test2
        )

    [topic_test3] => Array
        (
            [0] => 
        )
)

Am I missing something?