DIAGNOSIS Internal temperature sensor error or heat from the wall plate electronics biasing the reading. The sensor is located on the main logic board behind the display.
FIX Perform a sensor calibration. Go to thermostat settings > temperature > temperature calibration. Adjust the offset in +/- 1 degree increments until the reading matches a known-accurate thermometer placed next to the thermostat.
IF THAT DIDN'T WORK The thermostat may be installed on a poorly insulated exterior wall or near a heat source (lamp, TV, direct sunlight). Relocate the thermostat. This requires rewiring to a new wall plate location.
HEADS UP Calibration only affects the displayed temperature and comfort graphs. It does not alter the actual temperature at which the HVAC system turns on/off. The system still uses the raw sensor reading for control.