I contacted the developers direct support channel and they were great and fixed the issue for me. There seemed to be a theme related problem with the templates in WooCommerce.
Go to: WooCommerce > Settings > Emails > Order on hold
Then click Delete Template File
Save
Reload Decorator
and everything works again!
Also, the email is not in the middle of the email client, our width is set at 768, but it is displaying the padding for 600px so everything shifted to the right.
Here is link to a screen shot, also showing that the body text is different to the preview: https://drive.google.com/file/d/1QAO01KMArxN7uvqfFBbccNT8A3FAWHb_/view?usp=share_link
