Filtering a taxonomy term results by taxonomy term filter is not possible, because there is no assignment between them, like with posts. Posts can have categories assigned, but categories can’t have other categories assigned, thus can’t be filtered.
There might be a way to exclude the unchecked categories from showing in the result though, using a custom filter code. Do you want me to look into it? If I find a solution, can I add it to the functions.php file in your active theme directory via the FTP details? (that is the best possible location for a custom code)
I believe the reason why you don’t see any results when you only check Workers Compensation is, because those results are also within the Personal injury law category – which is unchecked, thus it tells the search to exclude anything that is within that category.
There is a very simple resolution to this, on the Frontend search settings -> Advanced panel, change this option: https://i.imgur.com/LL3SIWd.png
With this term logic, any post that matches at least one of the chosen categories will show up.
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