This is normal behavior of the unit.
The temperature displayed in the ONECTA app (history graph) is the one detected by the room temperature sensor located inside of the Air Purifier unit. This temperature can differ from the actual average temperature in the room because of several effects. For example, by laws of nature hot air rises, so the upper air layers of the room will be warmer than the average temperature. The difference in temperature will depend on the size and heat losses of the room, unit position in the room, its distance to the ceiling and the fan speed setting.
When the Air Purifier Unit is switched OFF, there is no airflow through the unit and hence the temperature measurement can be different.