Data was dropped due to too much outstanding data in rule “Microsoft.SystemCenter.Agent.MaintenanceMode” running for instance “site-scom.local” with id: in management group “Your Management Group.”

Resolve: If in a single management server environment, take the management server out of maintenance mode.

Never put a management server in maintenance mode: https://technet.microsoft.com/en-us/library/hh212718(v=sc.12).aspx

I am new to SCOM and recently started using ‘maintenance modes’ based on the following article:

https://technet.microsoft.com/en-us/system-center-docs/om/manage/how-to-suspend-monitoring-temporarily-by-using-maintenance-mode?f=255&MSPPError=-2147217396

My logic while flawed was to put the server in maintenance mode after applying updates and reboot. I left it in maintenance mode to resolve a couple of start up errors but all monitoring ceased. Take the server out of maintenance mode…and all was well…humbling… easy fix.