If I'm not logged in while browsing the forum I'm being asked for my u/name and password when navigating the forum. i.e just clicking a thread heading will take me to that thread but once there MicroB will throw up the login request. Also when I do log in, I'm asked to do so twice.
Could be a bug that's suddenly manifested itself in MicroB (unlikely as it's never happened before) or a stubborn bad cookie.