My Learning Thermostat has been working for 7 or8 years. Then yesterday I changed out my wifi router, but using the same network name and password. All was fine for 6 or so hours after the change. But in the morning the app says the thermostat is offline, yet the thermostat says it is online. The battery level was 3.8v, which is close to the max but I took it off the wall and connected it to a micro USB charger for a while (very slight increase) this had no effect. Then I reset the thermostat, still no effect. Then I removed the thermostat from the app and added it back, that all worked thought the app hung on the "you're all finished" page and after 30 mins or so I terminated (not just quit) the app (on iPhone), then started it and the thermostat now shows up. Will it last? I hope so (I have to say the sw side of Nest products is not great). My nest smoke alarms never came back online as did my other wifi devices (iDevices outlets/switches, ring doorbell, ring cameras) just the thermostat was an issue and maybe it had nothing to do with the wifi change, its hard to know.
But if having this issue (device says online while app says offline) the 3 things I can suggest are
* reset device (keep settings)
* make sure battery is charged
* remove and add back the device to the app
