Your taxonomy is set to 'hierarchical' => true, do you have the post included in both the parent and child category?
If you untick the parent category and only tick sub-category then it should use the first URL only.
Your taxonomy is set to 'hierarchical' => true, do you have the post included in both the parent and child category?
If you untick the parent category and only tick sub-category then it should use the first URL only.