Nest worked yesterday, now “no power” message

[NCWildcat]

Good morning- Our Nest was functioning fine for the five months we’ve been in our new house, but yesterday afternoon, it stopped functioning. There’s a no power error message (E268) that I’m receiving and I can’t seem to find the cure.  I changed out the batteries, restarted the Wi-Fi router, and reconnected one of the two floors on the Home app.  There weren’t any weather events or other house trauma, so I’m at a loss.  I looked at the fuse box as well, and nothing seems to have tripped any fuses.  Short of calling in a tech, does anyone have any other suggestions??

Thanks!
(also, for some reason, the Home app is having trouble reconnecting with the second floor thermostat, which also hadn’t happened before.)

[Rwiinbo]

Hi, NCWildcat! Just a few questions to help you. The common error E can sometimes (but not always) be a problem with your device's power supply, a disconnected cable, a cable plugged into the wrong socket, or a cable with a broken internal circuit (unlikely, but it happens). Could you please send us a photo of your error code and the model of your Nest Thermostat?