Diablo 3 was running normally until Battle.net Version is updated to the latest version after session 22. The game is now having a delay. Reinstalling both Battle.net app and Diablo 3 will resolve the issue on the first game, the delay will come back afterward.
I wonder if there is comparability issue on macOS 10.13.6 for the latest version of battle.net app or patch 2.6 on Diablo 3. I downloaded the battle.net app for Mac. After the installation, it will use the older interface (I assume it is an older version), then it will ask you to restart battle.net to install the latest update. The game (Diablo 3) run normally after the installation of battle.net before the latest update). Once battle.net is restarted with the latest update, the game will start having the delay again.
Battle.net Version 220.127.116.1112
Agent Version 18.104.22.16842