I tested this chatbot for a while and could not get to duplicate two API requests . I think that you may have already reconfigured the chatbot in such a way that you fixed this problem yourself. The only place where the chatbot sends an empty message is when calling a live-chat. But even such a message is not sent to the user, but only displayed in the chatbot, since the chat block contains message part.
Conversation that I tested, if you want to see https://chatbot.smart.botatende.com/live-chat/live-queue/67596
