You probably already know that occasionally chat will black out. Meaning the people already in it can see whats going on, but anyone who joins or refreshes cant. This is due to the following two symbols, I believe: < >
If someone in the chat says a sentence such as "No, it was not me <_<" chat works fine, so this bug might've been previously ignored. It wont black out until someone replies to this post, and even then, only for the new chatters and people who have refreshed.
As soon as you post in chat, however, it fixes, meaning it can be fixed by posting anything in chat, or PMing yourself.
If I'm not being clear, I'm sorry, but I can go into further detail if needed.