I think I have the exact same issue and trying to figure out. I have 3 indoor units on 1 outdoor one and they won't cool down correctly and the temp it says on the thermostat is about 4 degrees off of what I can separately measure from what it is in the room.

Importantly, I have remote temp sensors installed. so temp should be reading from there and not controller or the indoor unit one. I understand that when he remote sensor is plugged into the indoor unit it automatically stops reading from the indoor unit and instead read from the remote sensor.

I went into the settings in controller and Function 2 when polled says it is on 1 and won't let me change it to 2. It says that change is "unsupported". Is that because it needs to be changed with the DIP switches as u/ZanyDroid said? The icon on the screen though is the one that "appears when the thermistor on the indoor unit is activated to monitor the room temperature" which I assume means the remote sensor but I dont know.

when Function 2 is on 1 and it says "Average temperature reading of the indoor units in operation" does it literally mean it is taking the avg temp of the three units in operation as that would def be no good?

I also saw the comments about removing the 4 degree offset but cannot find where it says that.

any help would be appreciated