Thank you page notice automatically added to Body text

Hello,

I have a short note on my thank you page after checkout:
“Please have the order amount ready when the courier arrives to Pay on Delivery.
Your order is being processed and will be dispatched shortly!”

This text snippet is automatically added at the end of the body text of every mail that concerns order status plus customer invoice mail.
The text is not included in the body text and is also not shown in the mockup order preview. It just appears in previews of actual orders and in the actual mails.

Is there a way to fix this?

Cheers,
Stan