Mine is Am-Pro, serve well for many years but lately it takes abt 2 days to get to 45% every time i opened the door for a few minutes.
I'm not sure whether this is normal so decided to look for a new one.
Some dry cabs use drying agent like silica gel, just that the electric unit heats up and drys the agent. If your dry cab uses this mechanism, it is only a matter of them before the drying agent ability starts degrading.
You can either get a new dry cab, or see if you can swap out the dehumidifying unit. You can search taobao for the unit.