We came across an issue recently where we had placed a few servers into maintenance mode and when we stopped maintenance mode the servers did not change back to a healthy state, they were in a not monitored state.

We left it for an hours to see if the agent would sort itself out to no avail.

It appeared that the agent seemed to be stuck in the not monitored state, so what i did next was to try and refresh the agent was to put it into maintenance mode for 10 minutes and then stop the maintenance mode and within minutes the state changed to healthy again

Hope this helps

Daniel Davies