Symptoms
A script downgrade may fail and return the following error message when Cumulative Update 20 (CU20) is uninstalled from SQL Server 2017:
DateTime SpidNum Error: 935, Severity: 21, State: 1.
DateTime SpidNum The script level for 'system_xevents_modification.sql' in database 'master' cannot be downgraded from LevelOne to LevelTwo, which is supported by this server. This usually implies that a future database was attached and the downgrade path is not supported by the current installation. Install a newer version of SQL Server and re-try opening the database.
DateTime SpidNum Error: 3417, Severity: 21, State: 3.
DateTime SpidNum Cannot recover the master database. SQL Server is unable to run. Restore master from a full backup, repair it, or rebuild it. For more information about how to rebuild the master database, see SQL Server Books Online.
DateTime SpidNum SQL Trace was stopped due to server shutdown. Trace ID = '1'. This is an informational message only; no user action is required.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Resolution
This issue is fixed in the following cumulative update 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:
Workaround
To work around the issue, you can enable Trace Flag - T902, and then SQL Server will come online and script downgrade works. You don’t need to uninstall it again. To upgrade to a new CU, you need to remove this flag first.
References
Learn about the terminology that Microsoft uses to describe software updates.
