This monitor rolls up the data synchronization state of all availability replicas and checks whether any availability replica is not in the expected synchronization state. The monitor is in unhealthy state when any asynchronous replica is not in SYNCHRONIZING state and any synchronous replica is not in SYNCHRONIZED state. The monitor state is healthy otherwise.
In this availability group, at least one synchronous replica is not currently synchronized. The replica synchronization state could be either SYNCHRONIZING or NOT SYNCHRONIZING.
Find the availability replica with incorrect synchronization state using availability replica monitor state and resolve the issue at the availability replica.