Category snippet variable replacement not working

A very important feature of Yoast SEO is that you can automatically add SEO title and meta description templates to the homepage, all (custom) post types, all (custom) taxonomies, and other pages. You can create these templates with snippet variables, which we’ve listed in this list of available snippet variables in Yoast SEO.

If you’re using the Category (or %%category%%) snippet variable in your title template and that doesn’t get properly replaced with the category’s name, this is probably due to the fact that you’re using it for a custom taxonomy that isn’t really a “native” WordPress category. Simply replacing it with %%term_title%% will fix the replacement.

If the issue remains, you may need to use a custom template variable as discussed here.