

Ok, now I know why. without the +1 the automation does not trigger when the temperature is over the target and the TRVs running on idle. The +1 triggers the automation and switches them off until the room temperature is under the target temperature. So it does not explain why the mode is switched from heat to off or the other way around in the target +1° range.
Just bought an Tuxedo InfinityBook. Very nice piece of hardware.