Diagnosis
The unit is hitting its internal frost sensor. This happens when the coil gets too cold, usually in a cool room (below 65°F). It's a protective feature, not a fault.
How to Fix It
You need to raise the room temperature or move the dehumidifier to a warmer space. 1) Make sure it's not in a basement corner or right next to an AC vent. 2) Try running a space heater in the same room for a little while to warm the ambient air. 3) You can also try lowering the fan speed to "Low" if you have it on "High," as this can sometimes reduce how aggressively it cools the coil.
If That Didn't Work
Check the air filter. A completely clogged filter can restrict airflow so much that the coil freezes over quickly. Pull out the filter, wash it with warm water and mild soap if it's dirty, let it dry completely, and reinstall it.
Heads Up
This is very common in early spring or late fall in basements. It doesn't mean the unit is broken. If the room is persistently too cold for it to run, you might need a dehumidifier specifically designed for low-temperature spaces.