I have the same issue. I have tried numerous options I have seen in forums. Nothing has worked. I am able to start a new stream with the exact same attendees (8 others - all iPhones) and type a message to that new stream. The message is sent to participants and they see it in their original stream, while I only see it in the new stream. However, the text box re-appears on the original stream as well as remains on the new stream. I can continue then to chat on the original stream. Sometime within 12-24 hrs? when the system updates to the cloud? the new stream disappears and the text box on the original stream also disappears again, although all the messages typed by me on either stream are merged into the original stream. This has provided a work around to be able to respond to the original stream but is frustrating to do that every time to be able to reply into the stream.