Upon checking the page you’ve mentioned, you may want to look at the implementation of your H1 headings. While we aren’t familiar with your setup or themes or plugins as to how you’re adding the H1 headings, we do know if you are using the standard WordPress block editor that the post or page title at the top would equate as the H1 heading.

We would like to refer you to this articles that may help point you in the right direction – https://yoast.com/how-to-use-headings-on-your-site/ & https://yoast.com/whats-the-difference-between-an-h1-heading-and-the-seo-title/

We have Yoast premium installed – I’ve checked all the setting and they seem to be in line with that article.

I have a feeling it is something to do with the customization of the site, but at this point, I’m not sure what.