Servers seem to sync the friends list with each other, so this may be beyond me. There is a database script on the server handling the friends stuff, so that may be what the servers are using to communicate your list between each other but other than that I have no idea what is causing this to clear. I can possibly update it on Classic's side to not overwrite your friends list from another server's if it's empty, but that won't be able to fix accounts who have lost their friends. I'm not even sure if it'd resolve the issue(or if that even is the issue). I may have to talk to Stefan about it next time I see him.