Peter, for some strange reason there appear to be two different Message Centers:
One at the URL you provided (called "Backend 2.0"), another one at https://marketplace.reallusion.com/backend/message-center?tab=system-notification
(called "Backend 1.0") The latter one is the one you get to when you click any the notifications under the bell icon which is probably want the thread starter did.
Unless there is a really good reason for having these two Message Centers, I would suggest to unify the system and make it easier for people to navigate and manage their messages. Assuming that "Backend 2.0" is the newer system, I still think it could be improved.