A SELECT query that uses a batch mode hash aggregate operator that counts multiple nullable columns in the query execution plan returns incorrect results in SQL Server. This may occur when you use column store indexes, although it depends on the query pattern. For example, you may notice it for queries that use a PIVOT clause.
This fix is included 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.