why won't my messages come up on my mac anymore?

I'm having the same issue as well, the last messages to have been synced onto my Mac was from the beginning of this month since then nothing works. Apart from the fact that I am still able to send messages from my mac but unable to receive them. and now I'm slightly having the same issue with my phone where i receive messages late and once I've opened them and come out of my messages and go back again it disappears. - Apple is becoming extremely annoying, there is always one problem after another.

The same 😟 . Suddenly stopped on Mac Mini (Mavericks) while works well on iphone, ipad, macbook pro. Any ideas ?

Might be a corrupt .plist.

Do a backup, preferably 2 backups on 2 separate drives.

Quit the application.

Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library. Then go to Preferences/com.apple.iChat.plist. Move the .plist to your desktop.

Restart the computer, open the application and test. If it works okay, delete the plist from the desktop.

If the application is the same, return the .plist to where you got it from, overwriting the newer one.

If that doesn’t work, repeat the above but delete the com.apple.imagent.plist

Thanks to leonie and Ralph Johns (UK)for some information contained in this.

Also, may be worthwhile to log out of iCloud, wait a few minutes then log back in. Sometimes this kickstarts things.