Check the specifications for the sensor.
For instance, for the SHT31, at 100% actual humidity, the typical tolerance is +/- 2%, and the maximal tolerance is +/- 3.5%.
So, at 100% actual humidity, the sensor might be "saying" 97.5% humidity, or 103.5% humidity, or .......
And then, what is the external circuitry doing to adjust that measurement? Calibration?
And then, what is the display mechanism doing to adjust (or limit) the indication? Hint: most firmware-based displays won't show greater than 100% humidity.