In rare circumstances, when you execute a complex query that uses multiple joins, SQL Server 2017 may generate an Access Violation error when the new Adaptive Join feature is turned on (default).
To determine whether you are experiencing the Access Violation error because of the Adaptive Join feature, disable the feature by using Trace Flag 9398 at the session level. Then, monitor the program while you run these kinds of queries to determine whether the problem still occurs.
The fix for this problem is included in Cumulative Update 6 for SQL Server 2017.
About SQL Server 2017 builds
Each new build for SQL Server 2017 contains all the hotfixes and security fixes that were in the previous build. We recommend that you install the latest build for SQL Server 2017.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the standard terminology Microsoft uses to describe software updates.