Why people don't know that I sent them a message on chat? I also don't know that someone wrote to me if I first don't open the chat and click on a particular person. Before I had a notification if someone wrote to me, not any more!?

Do you mean you keep the chat bar closed?

No.  I have experienced this as well.  I cannot use the chat to talk to a friend unless we both happen to have a window opened to each other at the same time.  I had to call my friend on the phone and ask why he was ignoring me.  The chat has lost its notifications system.

Nope, it isn't closed. In chat options status is "I'm available" and I didn't disabled sound or popup notifications. However I don't hear any sound or see pink square with the number 1 when I have message.