https://support.microsoft.com/en-au/topic/kb4567837-fix-script-downgrade-may-fail-when-cumulative-update-20-cu20-is-uninstalled-from-sql-server-2017-0989680f-3f21-0879-b64a-0630fa02876a
KB4567837 - FIX: Script downgrade may fail when Cumulative Update 20 (CU20) is uninstalled from SQL...
FIX: Script downgrade may fail when Cumulative Update 20 (CU20) is uninstalled from SQL Server 2017