Could still be a software issue. Someone said this already but it could be possible that Lemmy.world is using a load balancer and multiple servers. These two servers' authentication tokens may be out of sync. So if you hit server 1 and you are sign in to server 1, you're good. If you hit server 2, you're signed out all of a sudden. This can also explain why the issue started to happen abruptly today. It's possible the load on the server wasn't that bad yesterday so the load balancer didn't kick in. This is all speculation. Will have to wait for an official message to confirm anything.
I am currently getting signed out every minute from lemmy.world. This is not a client side cache issue. I tested making API calls from the command line (with curl) with no cache and the issue still occurs. One call I get the correct response, the next I get a 400 telling me im not signed in.
Could still be a software issue. Someone said this already but it could be possible that Lemmy.world is using a load balancer and multiple servers. These two servers' authentication tokens may be out of sync. So if you hit server 1 and you are sign in to server 1, you're good. If you hit server 2, you're signed out all of a sudden. This can also explain why the issue started to happen abruptly today. It's possible the load on the server wasn't that bad yesterday so the load balancer didn't kick in. This is all speculation. Will have to wait for an official message to confirm anything.