I also experience this issue the other day - Thunderstorm in area, brief flickering of the lights (not sure my UPS even beeped...) but noticed later that Sense was offline.
A report or notification of Sense not "checking in" with the cloud services would be really nice as there was a period a month or so ago where Sense had been offline most of the month and I didn't realize it. I was just wondering why it was taking so long for it to recognize or characterize the devices within my home...
My sense is within the breaker panel with just the antenna poking out the bottom, so I don't have any visibility to any LEDs on the unit. May have to look into remounting it outside the cabinet.
I can verify it is definitely not a Wi-Fi Access Point or router issue, as I have had those on / off multiple times in doing other testing with work stuff and Sense always seemed to buffer the data and upload it when things came back online.