You can reproduce the issue here:
CREATE TABLE [dbo].[EmployeeDataMasking]( [RowId] [int] IDENTITY(1,1) NOT NULL, [EmployeeId] [int] NULL, [LastName] [varchar](50) MASKED WITH (FUNCTION = 'partial(2, "XXXX", 2)') NOT NULL, [FirstName] [varchar](50) MASKED WITH (FUNCTION = 'partial(2, "XXXX", 2)') NOT NULL, CONSTRAINT [PK_EmployeeDataMasking] PRIMARY KEY CLUSTERED ( [RowId] ASC )WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY], ) ON [PRIMARY] GO Insert Into dbo.EmployeeDataMasking (EmployeeId, LastName, FirstName) VALUES( 1,'Smithsonian','Daniel'),( 2,'Templeton','Ronald') Select EmployeeId, LastName, FirstName, LastName + ', ' + FirstName From dbo.EmployeeDataMasking
Notice the LastName and FirstName fields are partially masked (as expected). However, the combined name field contains the default mask. I don't know if this is considered a bug. However, I would think the combined field would retain the mask of the two fields it comprises. At least that's what I would prefer, since I don't know how to provide a mask for the combined field.