I'm pretty sure all of the games are hosted on one server. Either an update, a lot of connections leading to packet loss, which in turn, you are kicked from the server, or your internet connection.
Actually, there are more than one server. If you scroll down, it'll show you 'Games' and when you click 'Load Running Games' it should show you the servers.
Your definition of server is different from mine. I prefer to think of those servers as "instances". The server I'm referring to is the one that hosts the Roblox website, as well as the games.