Update:
I seemed to have figured this out by removing the back slash, but one other question I have is why is the email content getting clipped in Gmail?
As you have figured out, the break tag does not have a closing tag. It can be <br> or <br/> - but never </br>.
Gmail generally hides quoted content (like replies), so you only see the original content when viewing that message. Sometimes that can just be the signature, although usually it’s more. You cannot change this behaviour.
Thanks, my bad I for the wrong HTML format for line break.
Just on tables what is the support like for using these within the Content Type? Could there be any downsides to using tables in my use case? As trying to prevent the clipping issue.
Also when I paste my clean markup into the text box, it adds spaces between table elements which causes the email to come through with extra blank cells.