There has been a recent change, that after I connected (again) the app integration, it added all three thermostats (2 at one house, 1 at another) to both SmartThings locations. There used to be the option to select which device, which is no longer there.
The outcome is that all three devices are at both houses. This means, when I’m away from one, and at another, motion sensing from the occupied house is triggering an alarm at the house I’m not at.
After REMOVING the device from the wrong house, the connector is re-adding it every hour.