I'm just wondering if I'm using it wrong.
I thought that putting someone on /ignore meant that you'd never see anything they'd ever write unless you remove them from your personal the ignore list.
However, it doesn't seem like that does anything for me. I have to revert to using /mort to not see the text from someone.

...am I using it wrong?

yes u have to click there username and click ignore /ignore username is to un ignore them

I believe this is a known issue. It might relate to the community platform bugs, which you can report it here to see if they can help you: Topic-421545