leonardyudhistira on "Woocommerce : order Notes not showing up in the customer email"

Please kindly help me. I have an issue using the "Order Notes" feature.

https://docs.woocommerce.com/document/managing-orders/
Order/Customer Notes Section

It is mentioned in above FAQ that Order Notes will work. But when I apply it on my own order handling page, I found it was no success.

I have made some notes then clicked "Note to Customer" and then click OK. Then at last, I clicked "Save Order".

But sadly, in the email that my customer received, the Order Notes I have entered was not showing up (actually it must show up in a line before "Customer Details")

I have tried to modify the function.php according to the advice on this URL :
http://www.wpexplorer.com/woocommerce-order-notes-email/

After modify the function.php, even worst my page was stop working. So I restore it back.

Please help my with this issue. What should I do to solve this problem?

Many thanks in advance
Leonard