Hmm that is odd,
If I understand correctly the chat is not updating with the sent messages, (you click send, or press enter and the chat just stays empty), do the messages appear either on the client who sends them, or the server?
Screenshots of your blueprint setup would be helpful so that I help you figure out what is wrong,
Feel free to contact me either on skype: sarr_50, steam: sarr_50 (going under name Mr.Wolf) (I can help a little better over real time chat)