This happens frequently. I compose a message, hit "return," see that my message has been delivered, quit Messages, and then, hours later, relaunch it and find this
, i.e. that the text that had disappeared from the composition box when I sent the message has reappeared...except for the final period which is always missing.
Sorry, but I can't date it, although I don't
think it's been happening since November when I began messaging.