There was a vulnerability attack on certain Lemmy instances. As part of the resolution to the attack, all accounts have been automatically signed out. The client currently does not handle this gracefully so you will need to manually sign out and sign back in. I am working on a fix for this.
Thank you.
All JWT tokens should have been invalidated by the server creators. Those tokens should no longer be usable. It’s still possible actions were taken using your account while the server was compromised. See https://lemmy.world/post/1290412