What you use to measure temp and humidity are always suspect until you calibrate them. You should perform a salt test on the hygrometer. I've seen them off by well over 10% RH and then there are those that simply are broken. Perform a salt test to calibrate, takes bit over 4 hours with only 5 minutes prep. As for thermometer use a medical thermometer from medicine cabinet to calibrate the unit in incubator.
Salt test:
milk/juice or whatever cap filled with salt then add drops of water until saturated. Poor off standing water.
Put cap and hygrometer in sealed container. I use quart ziploc bag and provide small pillow of air.
Wait 4 hours minimum, 6 is better and take the reading of hygrometer. Subtract that from 75 for calibration #.
Ex. If your reading is 82 then 75-82= -7 You'd always subtract 7 from your readings for true RH.
Write the calibration on masking tape and stick it to incubator as a reminder.