By default, Easyblog will not render any HTML code into category description, so it can able to render the correct truncation content.

Imagine if the user add very long category description, it will show everything into this category header area and it not look nicely.

If you would like to include those HTML content, try download my attached file and replace into this following template override file location and see how it goes.

JoomlaFolder/templates/YourCurrentTemplate/html/com_easyblog/helpers/headers/category.php