Bad login on some servers

Well, I haven't played since last night, logged back in, went to multiplayer, clicked on the server I wanted, and it immediately told me "Failed to login: Bad Login"
I've confronted this issue before, but I'm not logged into my account anywhere (I'm the only one with access to it, and only use one server), aswell as followed the help on the support page, restarted my router, logged out and back in, etc. The strange part is, it's only for some servers. It says it's most likely computer->server problems, but it's there for some servers, and not there for some. My internet is fine, but this is quite confusing, and I frankly have no idea.