My 2 thermostats are ok when I only do settings in their respective areas. That is, when I make an adjustment on the upstairs thermostat it controls the upstairs and the same downstairs. My issue is the ID of each in the Home app. In the beginning I called the upstairs stat upstairs and in the app it controlled the upstairs. Same for downstairs. Somehow in the app now I must go to the upstairs stat to control the downstairs and the same issue to control the upstairs in the app.
The device information does list the serial number for example correctly so something has reversed things. I have wondered about the 6-digit code I still have which we had to enter at setup but now do not recall how or where to find it in the app.