Matrix Version: 18.104.22.168
I encountered the same issue with formatting custom form HTML email as in WYSIWYG breaking HTML in Custom form emails.
By following @Bart’s suggestion of using a paint layout, I’ve been able to format the HTML email as I need (i.e. only showing completed fields). This works perfectly when logged in. But when I submit the form as a public user, no output is sent in the email.
The custom form and the paint layout are live, and the Public user has been granted read permissions for both assets.
I’m using the Default Type format in the Paint Layout. And submission logging is enabled.
Are there some other settings I need to use?