I haven’t tested lemmy.world on my desktop since yesterday, but I had a weird issue on mobile this morning where it seemed I was both logged in and not logged in at the same time.

I ended up having to sign out, clear my cache, and sign back in to resolve the issue.

They say lemmy.world was hacked last night and part of their mitigation was to rotate a secret key number or something, very possibly the cause of the issue you’re experiencing.

TL;DR - Try clearing your internet cache then try logging in again. Good luck.