Once a player has left a game, then I cannot send any message in the chat box, I got a message error with the following code : C01T18R03X-0143686174005.
And I suspect that these are unexpected leavings, like game crash. Because it always happens in the middle of a game.
I think it is related to a closed (but unsolved) topic : Error sending message in chat
By the way, the chat box is still laggy, while the problem has been reported few months ago… (Messaging interface is too laggy in multiplayer!)