OK, this looks bad and unfortunate for us - this is really our problem, this state is not "grey" (health service outage), this is a "white" state (Unmonitored), which means that monitor failed to initialize for some reason. It could be performance-realted issue (our MP has a little bit more workflows than Microsoft's, plus I beleive when you are looking onto this Hyper-V Host Computer state, you are seeing Windows Computer object which has minimum set of monitors)
You can restart the Health Service, which is Microsoft Monitoring Agent or System Center Monitoring Agent, it's not affecting Hyper-V.
If the situation remains we definitely need to check the Operations Manager event log, there should be clues on why our workflows are failing. Did you previously see anything like this or only VM migration "sparkled" the issue?
I would appreciate if you can open a support case with our tech support team (you can send me a ticket number), we can arrange a webex to understand what is happening on your Hyper-V hosts. I'm sure we can make our MPs to work correctly.