Your article text will contain html tags that are not permitted inside the <h3> tag, like the <p> tags.
You should remove any html tags in the output, like:
If you need the html tags inside the article - like those - field-value spans, then you shouldn't be placing it in a <h3> tag.
If that is just for styling purposes (ie: make the text bold and bigger), use css via a div with a class.