Symptoms
Assume that you have at least two secondary replicas in AlwaysOn Availability Groups (AG) in Microsoft SQL Server 2016 or 2017. When you run the system function sys.fn_hadr_backup_is_preferred_replica on secondary replicas to determine whether the current replica is the preferred backup replica, it returns TRUE for more than one secondary replica even if the priority values are identical.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Resolution
This issue is fixed in the following cumulative updates for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
References
Learn about the terminology that Microsoft uses to describe software updates.
