Category’s showing all posts

I’ts very difficult to troublehsoot from the front-end bc you’re not printing out the Category on the Cateogy index page, i.e. :
https://vet2pet.com/category/leadership/

I have to actually click into each blog to see, then visually compare.

Can you verify that this post does not have the Leadership Cateogy applied in the backend?
https://vet2pet.com/wp-admin/post.php?post=10300&action=edit

Also, what does the Count column look like on your Categories page?
https://vet2pet.com/wp-admin/edit-tags.php?taxonomy=category
In other words, is WordPress recognzing the Posts and Associated Categories.

You could also try adding a Category base:
https://vet2pet.com/wp-admin/options-permalink.php

At worst, you could create your own index page per Category, like this:
https://www.wpbeginner.com/wp-themes/how-to-create-category-templates-in-wordpress/

Yes.
You need to verify that this post does not have the Leadership Category applied:
>> https://vet2pet.com/wp-admin/post.php?post=10300&action=edit

I’m going to assume you are using native WordPress Category landing pages and not an Elementor module to output these posts (on /category/leadership for example) ??

If you are using the native WordPress Category function, then I would reach out to the theme developer:
https://www.holgerkoenemann.de/mehr-ueber-mich/
However, the theme is under serious drama right now:
https://github.com/understrap/understrap/issues/1258

I would post to the issue queue in GitHub:
https://github.com/understrap/understrap/issues

Ok, then I would put my bet on something wrong with the theme.
Load a default WP theme, and see if the categories links work as expected.
https://en-ca.ww.wp.xz.cn/themes/twentytwenty/

If not, check your Category permalinks. And your htaccess file.