A bit late of a reply, but I found the answer to this today while getting the same issue. 

The details are being saved on another template design, which is pulling through on your emails but not showing in your template amendment previews. It probably happened during the initial set up where the first template design Airy New was used to create the look of the invoice before you switched over to a different design, which is what happened to me. 

1. Go to custom form styles in settings

2. Edit the template

3. On design, click change up the template & click through all the templates until you find one that shows the EFT details that are causing the error - in my case, I was using the Friendly design but Airy New was the cause of the issue. So select that troublesome one (Airy New) & select add your EFT details.

4. Delete out these / amend them to the correct one & save

5. New details are updated & you can move back to your preferred template now. 

Hopefully, this helps someone else too!