I was experimenting (with a local Wordpress installation) a little bit with Upfront just to get confident with it.
I need to use a plugin to share snippet of code and I'm trying Crayon Syntax Highlighter which I think it's great for my purpose but I can't really understand how to integrate it with Upfront.
If I just create a new post and embed into the post the snippet of code and when I preview the post, the snippet is showed in the wrong location and an error message is added to the post. Visiting the page live, the Crayon widget is showed without any content and the error message persist.
Using a different theme (Twenty Seventeen), the problem is solved as you can see from the attached screenshots.