Consider the following scenario:
You use the AlwaysOn Availability Groups feature in Microsoft SQL Server 2012. FILESTREAM is enabled on each instance.
You create a listener for the availability group, and your application accesses the filestream data by using listenername\MSSQLSERVER. MSSQLSERVER is the name of the Windows share that's specified under the FILESTREAM tab in SQL Server Configuration Manager.
You apply SQL Server 2012 SP2 on the secondary replica, and as part of a rolling upgrade, you failover the primary replica.
You try to access the filestream path by using the Universal Naming Convention (UNC) path in File Manager, for example, listenername\MSSQLSERVER.
In this scenario, the access to the UNC path of the FileStream data fails, and your application can't access the FileStream data.
The issue was first fixed in the following cumulative update of 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. We recommend that you download and install the latest 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.