The menu after Alt+Tab

Open ESC → Settings → Interface and find Open ESC menu when switching windows (Alt+Tab). It is enabled by default. Turn it off if switching to another window should not open the ESC menu. Your choice is saved between game sessions.

Mouse movement does not control the game camera while another window is active. Returning to the game should not turn the camera because of mouse movements made on the desktop. You can still open the menu yourself with ESC.

Losing the connection

When the connection to the server is lost, the client blocks gameplay and shows options to reconnect or quit. Shutting down a server does not move the player to a local copy.

A network warning does not always mean that the server is overloaded. A broken connection or a pause in incoming data can also cause it. If it keeps happening, report it in Support with the server name, time and game log.

The client_lost error

client_lost means that the launcher did not receive the game client's heartbeat in time. It does not identify the cause of the freeze on its own. Keep the log file named in the error window and attach it to a Support report, especially if the error happens while starting the game.