In Messages, all of my buddies have disappeared from the buddy list. ***?

Question

I video chat with a friend using Messages and suddenly my buddy list is empty .... no buddies.  We both use AIM.  What gives?

Answer 1

Hi,
Your Buddy List is kept on the Server for AIM.
This does mean that if you have two Logins at the same time it is pretty much impossible to do anything with the Buddy List as the other login will tend to "Correct" things.
This can mean if the second login is set to Invisible then all your Buddies will appear Off line.  (if one login does get full dominance).
You may end up with a situation where neither login maintains dominance and you may only see those Buddies that are Off line at their ends but not see the ones that are ON line either.
However this is only a possible outcome and would take loads of testing over different types of login to see if it were possible.
Other Login include Different apps on the same Mac
The same and different apps on different computers.
PC logins.
Logins via iOS devices
Logins on other type of phones
Web Browser logins.
You can also test non Apple IDs on this page https://settings.aim.com/
Apple IDs (@mac.com, @me.com linked to iCloud and @icloud.com IDs)  use a sort of two pass Login to AIM and Apple to use the Apple Password for the IDs to work.
This now excludes the use of @mac.com name on earlier versions of iChat.
The iMessages account uses an Apple ID.
It appears that it does have to be an iCloud variant (new Apple IDs are automatically iCloud ones but older ones may not be).
The ID does NOT have to be the one used in the iCloud Setting.
In fact iTunes and App Store are best served by the same ID but they can be different (it requires two payment methods).  FaceTime and Messages (iMessages Account) are also best served by the same ID as you can switch to Video or Audio in FaceTime from the iMessages account. Again they can be different and you could be using 4 different IDs up to here.
Then there is the iCloud settings in System Preferences the links to iPhoto, Contacts, Calendar, Reminders, Notes and so on (BUT NOT iMessages) that syncs those apps with your other Macs and iOS devices.
Your Apple ID used in iMessages needs to be able to check the password at Apple and if it is the same one you use for iCloud that is a close as it gets.
The iCloud server could crash but iMessages would handle it's own login.
(If the server Apple uses for Apple IDs in general were to crash that is a different story but that is going to be a server farm an unlikely to fail in that sense.)
If your iCloud Account is syncing Contacts then all the devices that are linked to that need to be still syncing.
It is a bit unclear if one device is a Master device or if the list is completely moved to the iCloud servers.
I have found if the Sync is turned Off on my Mac there is no Local Contacts List.
However whilst you might not see First Name Last Names (or your choice) in the Buddy Lists you should still see the AIM names (AOL or AIM IDs/Screen Names and other Apple ID used as AIM names)
Checking on the AIM Settings page may also reveal if the account you have with AIM has been suspended.
This can happen if you travel and AIM deems the use "Unusual".
Since Apple IDs can no long be checked there it has become more difficult to obtain a full picture.
9:29 pm      Friday; February 20, 2015
​  iMac 2.5Ghz i5 2011 (Mavericks 10.9)
 G4/1GhzDual MDD (Leopard 10.5.8)
 MacBookPro 2Gb (Snow Leopard 10.6.8)
 Mac OS X (10.6.8),
 Couple of iPhones and an iPad