When Dynamic Data Mask (DDM) is used with queries that have User Defined Functions (UDFs) in SQL Server 2019, incorrect type of data mask is 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 update for SQL Server:
Each new cumulative update 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:
Learn about the terminology that Microsoft uses to describe software updates.