The subfields first_name and last_name cannot be saved.

Hi,

My registration form does not allow me to save my first and last name.
I am using mb_user_profile_register to display the MB User Profile custom fields as follows.
Is it possible to make this work correctly with subfields?
By the way, I was able to save "last_name_kana" and "first_name_kana" correctly.

[mb_user_profile_register id="user-profile" form_id="form-registration" email_as_username="true" password_strength="false" label_submit="送信する" confirmation="登録を完了しました" label_email="メールアドレス" label_password="パスワード" label_password2="パスワード（確認用）"]

<?php
add_filter('rwmb_meta_boxes', 'your_prefix_function_name');

function your_prefix_function_name($meta_boxes) {
    $prefix = '';

    $meta_boxes[] = [
        'title'  => __('会員情報', 'your-text-domain'),
        'id'     => 'user-profile',
        'type'   => 'user',
        'fields' => [
            [
                'name'   => __('ご担当者名', 'your-text-domain'),
                'id'     => $prefix . 'group_name',
                'type'   => 'group',
                'class'  => 'row-name row-required',
                'fields' => [
                    [
                        'name'       => __('姓', 'your-text-domain'),
                        'id'         => $prefix . 'last_name',
                        'type'       => 'text',
                        'required'   => true,
                        'attributes' => [
                            'placeholder' => 'ご担当者名 姓',
                        ],
                    ],
                    [
                        'name'       => __('名', 'your-text-domain'),
                        'id'         => $prefix . 'first_name',
                        'type'       => 'text',
                        'required'   => true,
                        'attributes' => [
                            'placeholder' => 'ご担当者名 名',
                        ],
                    ],
                ],
            ],
            [
                'name'   => __('ふりがな', 'your-text-domain'),
                'id'     => $prefix . 'group_name_kana',
                'type'   => 'group',
                'class'  => 'row-name row-required kana',
                'fields' => [
                    [
                        'name'       => __('姓（かな）', 'your-text-domain'),
                        'id'         => $prefix . 'last_name_kana',
                        'type'       => 'text',
                        'required'   => true,
                        'attributes' => [
                            'placeholder' => 'ふりがな 姓',
                        ],
                    ],
                    [
                        'name'       => __('名（かな）', 'your-text-domain'),
                        'id'         => $prefix . 'first_name_kana',
                        'type'       => 'text',
                        'required'   => true,
                        'attributes' => [
                            'placeholder' => 'ふりがな 名',
                        ],
                    ],
                ],
            ],            
        ],
    ];

    return $meta_boxes;
}

Best regards,
Yumikom