Since this morning every time I click a link in the main chat that leads to a forum topic it automatically subscribes me to it. Then I end up getting notifications clogging up my mailbox until I go back to the topic and unsubscribe.

I`m having this issue again.

I think this probably happens when someone subscribes to the thread themselves, then posts a link in chat. The subscription tag remains in the URL.

Yes. The '&s=y' at the end subscribes you automatically.