Likely there's nothing wrong with the hygrometer (although, impossible is nothing), but rather your expectations need some adjustments.
A dry cabinet is not a shock freezer where you turn on power and 15min later "Ding" it's done. The process of lowering the humidity inside takes a few hours, more than 24h is not unusual depending on the environmental conditions in your place (e.g. whether you use aircon or not), the size of the cabinet and the humidity of what you put inside (dry cabinets are not meant for cameras only).
So put in your equipment, adjust the cabinet to target humidity of about 45% (or: if you have AD series, turn the knob somewhere between green and red area) - and wait! Come bac checking after 6h and you should see some progress. Wait at least for another 24h before you make further adjustments. Humidity should be equal or lower 45%. Lower than 45% is also fine, nothing to panic. In the meantime do yourself a favour and read the manual and the many similar threads here about dry cabinets. Search function is upper right hand, help yourself.