Sorry to hear about your experience with your Nest thermostat and for the delayed response.
A few questions — were there recent changes made on your HVAC or Nest thermostat before this started happening? Does the change happen randomly or does it happen on a specific time of the day? Also, could you try the suggested steps on this link then let me know what happens?
It looks like we have come to a solution so I'm going to be locking this thread. If you have any other concerns or questions, please feel free to create a new thread.
Have a great day.