I'm unable to add the dummy <body> element as I am unable to change the message content due to it being sent to us from a client we are working with.
I have tested sending a chat message from Spark to a user that is offline and it is working.
I don't think that is the ghost session issue as I had this same problem with 3.9.2. I was hoping upgrade to 3.9.3 would solve my problem, which as we can see it didn't.