The temperature value will affect the result of humidity.
If the temprature sensor already shows some offset compared to reference sensor, then the humidity deviaiton is expected here.
The temperature sensor accuracy typical value is around 0.5 degrees according to spec.
So i will suggest you to check again the environment if they are close environment and achieve the homogeneous of whole environment, which means in each location of this space you have same temperature and humidity.
BTW, 8% is still within the tolerance range of BME280 relative humidity output.