This may be relevant for people using G4+share or G5: Sunday, January 10, 2016, Dexcom Share server is temporarily down, so at this time you won’t be able to see CGM data on any devices that depend on connectivity to the server, e.g. Follow app or smart watches. In general, here you can check status of the Dexcom share service.
Update: as of 1pm MST (1/10/16), the Share service is up and running again.