There's two ways to "ignore" a person.
You can block them from sending you pms or you can block yourself from seeing their posts.
Which do you want to do?
If you just want to block them from sending you pms, have your "my ignore" settings look like this....
Ignore Filter Disabled To block public posts from ignored people, make sure this is Enabled.
Replies To Ignored People Shown To block replies to posts from ignored people, make sure this is Hidden