"This server lost your connection."

This error is used in a few places (on my to-do to add specific error messages), but they are all fairly similar:

• When establishing a connection with the server your client did not get any response after 30 seconds.
• After loading the level and asking the server to log in your client did not get a response after 10 seconds.
• During gameplay your client went 30 seconds without any messages from the server.

Usually connection loss is caught sooner in the network transport library with a different error, so this error suggests the client or server froze/hitched for a long time. If you noticed your screen froze and you stopped moving that means the hitch happened on your client, whereas if you kept moving and everything else froze that means the hitch happened on the server.

If your client hitched it might be related to some content used by the server like very high-detail models or custom menus, or a performance problem in the base game.

If the server hitched it is probably a plugin-related bug. In particular doing database queries (e.g. MySQL) on the main thread is a common cause of disconnecting everyone on the server.