Tim has been trying to help me get back the ability to type in the message box so I could reply and post again after it stopped working a week ago. We noticed other people having this frustrating malfunction too so I promised I would post a solution when I found one!
I have no idea why but when I tapped that aA at the far right of the top line of message window buttons I could finally tap a space marker line into the window and type again. It sporadically needs to be tapped to allow typing when replying to another thread.
I hope this helps others. I don't even know what that symbol is supposed to be for.<3 Jeanée