When you use Cumulative Update 3, Cumulative Update 4, or Cumulative Update 5 for SQL Server 2016 Service Pack 1, a query that uses a parallel query execution plan that contains a merge join operator may take longer to execute with extremely skewed data.
This fix is included in the following cumulative updates for SQL Server:
Cumulative Update 2 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 cumulative updates for SQL Server:
Latest cumulative update for SQL Server 2017
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology Microsoft uses to describe software updates.