chuckfromchapel hill,
If syncing messages via iCloud is a feature that has just been set up, are you able to test whether this is happening with both newly received messages (since setting it up) and older messages that existed prior to setting it all up?
Access your messages on all your Apple devices
If this is just being setup on your Mac, here is another step we can take -
“After you turn on Messages in iCloud, your messages stay up to date automatically. If you want to make sure a new change takes effect immediately, choose Messages > Settings, click iMessage, click Settings, then click Sync Now.”
Thanks.