With the new section headers released on October 22, 2019, when the header is enabled with the icon image and then the section is sent as an email through an Automation action, the icon image shows a broken/missing image instead of the image itself.
I believe this is a limitation of SMTP and/or the HTML sanitation happening on the email client. The icons are SVG format and that will never fly in SMTP.
To remedy this, I think the images have to be conveyed as Base64 strings or actual PNG URLs and such URLs to the icon images must be openly accessible for rendering outside the security context of the Coda document.