I have never once activated this "ignore boards" feature. However, just now I clicked into "replies" and the entire screen shows me nothing. And then just now I clicked into "unread posts" and again the whole screen shows nothing. ...
I don't think this is related to the "Ignore Boards" feature. Either the forum is acting up (which it might do, if the database has acquired a glitch), or it's acting normally and you've run into one of it's quirky ideas about what "normally" is.
"Show unread posts since last visit" sometimes has a very odd idea of when your last visit was. This has something to do with "sessions", which are a mechanism the forum software uses to keep track of you. I've never read a good explanation of how "sessions" work, but sometimes they are shorter than one visit, and sometimes they encompass several visits. So sometimes the list of unread posts is very short and sometimes it's very long. AFAIK, we can't do anything about this quirk.
"Show new replies to your posts" usually works the way you'd expect. But if you have, in fact, looked at every thread where somebody has replied to one of your posts, this list will be empty.
Anyway, that's what should happen if it's working right. If it's not working right, we probably need to run a database repair.