Billing First Name is not working for Order Details

I was checking with different order statuses as well as customizing email templates with my child theme. I added the following code to “customer-processing-order.php” and “customer-on-hold-order.php” file before the order table to display customer’s full name:

<h1>Hello <?php echo get_post_meta($order->ID,'_billing_first_name', true); ?> <?php echo get_post_meta($order->ID,'_billing_last_name', true); ?>,</h1>

When I create a new order, the email correctly displays both first and last name. However, when I go to woocommerce->order and try to change status of that order from “processing” to “on-hold”, the billing first name disappears from that order details page. Also, the email will not display first name and will only display last name. Billing First Name isn’t coming back now whichever order status I set it to from that point.