Monitors showing as critical in Active Alerts, but in health explorer showing as Healthy

I have a newly built SCOM 2012 R2 Environment 3 Servers, 

SQL Server 

Management Server

Datawarehouse Server

SCOM 2012 R2 was monitoring fine, and is picking up my servers etc, 

Although since a recent DataCenter power outage, all of my SCOM Active alerts aren't automatically clearing them even though the monitor is showing as healthy in Health Explorer.

I have tried the below to no avail:
Reinstalling the agent on all clients this shows no errors.
Resetting via Health Explorer
Manually restarting the Agent on each client
Double checking the Monitor has the "Automatically Resolve" tick box checked

The majority of these Monitors are relating to Exchange Management Pack 2007. If you need more information please let me know.