This is partially a problem with how Lemmy works at the moment. Ideally, all communities should be synchronized and shown on all instances/servers, as of now any new severs from other instances will only show up on your own instance after the first time someone from your instance subscribes. This means someone has to manually type in the url and subscribe to an external community from your own server/instance so that your own instance can “discover” that the community exists and add it to the list. Hopefully this gets better down the road—I’m sure it will—but in the meantime https://lemmyverse.net/communities is a great place to discover new communities.
I’m working on a client and have noticed programming.dev has issues with login fairly frequently, while other instances like lemm.ee and lemmy.world do not. It only happens per-IP address so it might have something to do with rate limiting or blocking suspicious clients that connect. Hopefully this can be fixed down the road.
I am working on a Lemmy client and have noticed that the Login system is secure, but it isn’t very robust. Usually, there is something called a “refresh token” provided that automatically verifies users and lets a user stay logged in indefinitely. Lemmy doesn’t have that implemented at this time, so eventually you will be logged out by your browser as a security measure when your cookie expires and you will have to log in again. For Safari, the maximum time is 7 days before you are logged out.
So, until Lemmy implements refresh tokens or similar, this will probably be how it is on most browsers and Lemmy clients.
This is partially a problem with how Lemmy works at the moment. Ideally, all communities should be synchronized and shown on all instances/servers, as of now any new severs from other instances will only show up on your own instance after the first time someone from your instance subscribes. This means someone has to manually type in the url and subscribe to an external community from your own server/instance so that your own instance can “discover” that the community exists and add it to the list. Hopefully this gets better down the road—I’m sure it will—but in the meantime https://lemmyverse.net/communities is a great place to discover new communities.