Thanks for reaching out to the Google Nest Community and sorry for the delay. I want to dig deeper into this.
A few questions — what specific type of Nest thermostat is this? How big is the difference between the readout of the Nest thermostat and your thermometer or other thermostat? Also, do you have other active Nest thermostats? If yes, are you experiencing the same? It would also be great if you could provide a rundown of the steps that you've already tried so we can pick up from there.