By Marnix Wolf
Just checked the
KB3209604 tells more on CU#12 for System Center 2012 R2 as a whole and refers to KB3209587 for more detailed information about UR#12 for SCOM 2012 R2 specifically.
Taken directly from this KB article, this is what UR#12 for SCOM 2012 R2 fixes:
When you try to upgrade System Center 2012 R2 Operations Manager Reporting Server to System Center 2016 Operations Manager reporting server, the upgrade fails for the following configuration: Server A is configured as System Center 2012 R2 Operations Manager including Management Server. Server B is configured as System Center 2012 R2 Operations Manager, including Operations Manager Database (OpsMgrDB), Operations Manager Data Warehouse (OpsMgrDW) and Operations Manager Reporting Server.
( X ) Management Server Upgraded Check
The management server to which this component reports has not been upgraded.
Recovery tasks on “Computer Not Reachable” messages in the System Center Operations Manager Monitor generate failed logons for System Center Operations Manager Agents that are not part of the same domain as the Management Groups. When a Management Server is removed from the All Management Servers Resource Pool, the monitoring host process do not update the …read more
Read more here:: Thoughts on OpsMgr and System Center 2012