Hi there,
After inspecting the element it seems you’re putting html as title of the category for which it’s loading error as we validate or esc html while rendering it won’t show any html code instead it’ll show as simple text. Please try to fix the title.
If you check in our demo the category page is loading perfectly with the category title inside h1 tag. https://themes.themeregion.com/trade/ad_category/books-magazines/
If you’ve done some customization or something then this might also cause such thing. Checkout the solution that I told you. Thanks.