That happened due to the emoji vulnerability. One mitigation step admins had to take is rotate JWT secrets, which essentially deauthenticated everyone’s sessions.

Lemmy-UI and some 3rd party applications didn’t know how to react to that, as this is not an official Lemmy feature (it required a database query), so they stayed in that limbo state you’re describing here.

Just log out and back in. If the problem persists, delete the cookie for your instance and try again.