APB Zone Alarm:
When anti-passback fails because a user tries to enter through the same door again after authentication success.
APB Zone Clear:
When you release the alarm (allow users to enter again) in the Zone Monitoring menu.
When you set the APB setting of 'In case of Disconnected' to Door Close, Zone Disconnected message will appear when the slave and master device lose connection.
Since you set the door to be closed when the slave device is disconnected with the master device, the door will not open even on authentication success on the slave device.