I'm not receiving new messages in the Messages app on macOS (High Sierra). I do get notifications of new messages there (delayed many minutes from when I receive them on iOS). And I can send messages from macOS (which appear immediately on my iOS Messages and at the recipient). But no new Messages of any kind appear in Messages on macOS.
Is there a way to totally and completely reset Messages on macOS so that it works again?
(Note that despite failing to be of any use, Messages on macOS renders the machine unusable when running by maxing out CPU usage. So perhaps a clean resent of Messages in necessary to fix that as well?)