Text Syncing Suddenly Stopped

Until Oct. 20, 2018, text messages were synced among my iMac, iPad, and iPhone. Suddenly, some messages are no longer syncing. Some are but certain texts are being missed because they show up on one device but not the others. I've followed advice about this from previous posts but nothing is helping to get texts to sync consistently. Is this related to the new IOS update? What to do?