So if you got to "security filters" and in the spammers tab and hidden words tab, you will see nothing in those lists (unless you've blocked some words). But there are things in those lists you can't see. Every now and then you might get a notification from someone that disappears, or a quote reply from one of your follows quoting someone and it says "this message is hidden, click to show" or something like that. If you go to that profile, you'll see where it usually says follow it says unblock. If you unblock, it automatically reblocks it immediately.

Amethyst is blocking people and words for you, without your knowledge or permission, and sharing this block list with other amethyst users and auto updating it. People are shafown banned from amethyst.