Recently lemmy.world and other big lemmy instances were compromised - attackers used an exploit to steal admin JWTs (json web tokens), and started changing settings and posting as admins. JWT is created when you log in, and is passed during all interactions to prove who you are.
To recover from the compromise, lemmy.world invalidated all the existing tokens and forced everyone to log in again. Unfortunately lemmy.world stopped trusting valid JWTs too, and apps all had some crazy behavior.
This was resolved as of Wednesday some time, I think.
My advice is to make sure your apps are all updated, and log out / back in to each of them. If it’s not resolved for you, try deleting and reinstalling the apps. If it’s still not resolved, search for a lemmy support community as another poster suggested.