Symptoms
Assume that you use Always On Availability Groups in Microsoft SQL Server. After you switch to serial redo from parallel redo by enabling Trace Flag 3459, serial redo works as expected. However, when you switch back to parallel redo by disabling Trace Flag 3459, parallel redo does not work. If you restart the instance of SQL Server, parallel redo works as expected.
Resolution
This problem is fixed in the following update for SQL Server:
Cumulative Update 9 for SQL Server 2017
About SQL Server builds
Each new build for SQL Server contains all the hotfixes and security fixes that were in the previous build. We recommend that you install the latest build for your version of SQL Server:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology Microsoft uses to describe software updates.
