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.

Anybody else?

Yes, I see the same effect, no period at the end. Question marks and exclamation points do show up, though. I also see it in messages going back into 2019. Odd indeed.

Thanks for confirming the odd behavior, Ira.

I guess maybe it's been happening since I began messaging without my having realized paid attention to it and is not new.