Assume that you are using Dynamic Data Masking (DDM) on a column in Microsoft SQL Server 2016 or 2017. When you use PIVOT or UNPIVOT function on the column which is masked, the data masking may not be applied.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
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: