I realize this is a late post, but we recently ran into a similar problem and it occurred after a maintenance update to the cloud platform. What we found was that the front-end servers were relocated to an IP address which (according to our GeoIP filters on the firewall) is based in Germany. We were blocking Germany, and therefore the devices would not show in the cloud. One of those things you don't always think of, especially when it occurs on a device for which you don't "see" where it's going from a contextual sense.
BigRic