Symptoms
CASE expressions containing identical sub-queries that are executed in SQL Server 2017 may return incorrect results.
Resolution
The fix for this issue is included in the following update for SQL Server:
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 build for your version of SQL Server:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the standard terminology that Microsoft uses to describe software updates.