I received in my last game a warning that I may be punished if I again leave the game, but actually I didn't. I was waiting for my opponents move, and when the opponent made finally a move, I received immediately this warning. As a matter of fact, first I saw the warning and only then the move, but I couldn't make my move any more because the game was over!!! Maybe I lost my connection, but I was not aware of that. It was very frustrating because I thought I had actually a better position, or at least equal.
https://lichess.org/1aiol6nWeK5t
I was black in this game.
There is Lichess feedback forum for such an issue.
Thank you for the tip. :-)