Researching like you but my understanding is one nest thermostat and
heatsink per zone. Max of 20 zones per home. I think the temperature
senders are more about getting a range of readings from various points
around a larger zone so the thermostat ca...
Check to see if it's the Legionella protection function kicking in...
More details
here...https://support.google.com/googlenest/answer/9256656?hl=en-GB