Desiccant dehumidifiers have a built-in humidistat that controls the units' operation based on the detected Relative Humidity (RH) level in the room.
In "auto" and "low" modes, it will dehumidify the air down to 55%RH, or 45%RH in "high" mode, and 35%RH in "turbo laundry" mode.
Once they reach that humidity level, they will turn themselves off and then check the relative humidity once every 30 minutes to see if the relative humidity has increased.
Therefore, if your unit has stopped operating, it could just be because the detected RH Level in your room is already below the preset mode.
You can check the Ionmax ION612 and ION632 Control Settings here