Devices not reporting on

I have multiple devices that never report that are “online” and always off. I have sat at these desks and verify they are on only to never see them show up active/online. What can I do about this?

I had a couple of endpoints showing as offline since mid Dec… Manually stopping the ITSMService and restarting it fixed the problem… To be more specific, both had frozen during CCS updating at around 30% and even a reboot wouldnt sort it. When I stopped the ITSMService, the updates immediately completed then I restarted the service and the endpoints came back online. Could be related. Of course this meant a site visit