You run the sys.dm_hadr_availability_group_states dynamic management view (DMV) against a secondary replica of a Microsoft SQL Server Always On availability group. In this scenario, the DMV always displays "NOT_HEALTHY" in the synchronization_health_desc column even when the replica is healthy.
This issue is fixed in the following cumulative updates for SQL Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Article ID: 4013111 - Last Review: May 15, 2017 - Revision: 15