HTML tags not mixing with markdown

For styles that are can not be done in Markdown, you're supposed to be able, in most cases, mix html tags together with the Markdown. However, on my site I have tried this and what happens is the html tags show up and the styles are not applied to the text, but the markdown is. I've done a Google search and tried everything suggested, but nothing works. The only things that work are the markdown styles.

I have even tried using the markdown="1" in blocks and that doesn't work either.

When I first started mixing the two, it was working, but then after some time the html tags began appearing in the text. Maybe there is some config file that needs tweaking?

Why is this happening?

I think it would be much easier to understand the issue if you provided examples of your content MD file, what you get, what you expect and what's you yaml config for content parsing