Out of the blue, thermostat disappeared from my family member’s nest app. I tried all directions provided by google, to find the entry key, there is no scan code, on the back of the base. When I chose Nest app in the settings, it did not provide the entry key.
what did work was as follows: I logged out and logged back in, using google account, after two or three trials, nest logged me in and along with the thermostat.
Answered! Go to the Recommended Answer.