Hi. Your humidifier controller looks a lot like the
Hughes 1UHG3 wall-mount room humidifier controller, though it could be a different make and model. The model I linked to, above, doesn't have a remote sensor, and measures the humidity where it is plugged in. You didn't mention how you have it setup. Is your humidifier controller setup inside your cure chamber (plugged into an outlet or extension cord inside the cure chamber - some people use this controller that way)? If not, is it setup outside your cure chamber with a remote sensor inside your cure chamber?
If your hygrometer is measuring the humidity inside your cure chamber and your humidifier controller is measuring the humidity of the room outside your cure chamber, that could easily explain a 20% difference between the two readings. Just a thought.