DIAGNOSIS: It's hitting its internal full-tank safety. The unit collects condensation and will shut off to prevent water spillage when the reservoir is full.
FIX: Drain the internal tank immediately. Unplug, carefully move the unit to a location where you can access the back. Remove the rubber drain plug (lower back, near the bottom). Let all water drain into a pan. Reinsert plug firmly.
IF THAT DIDN'T WORK: The unit may be overheating due to a blocked air intake or exhaust. Ensure the air filter is clean and nothing is within 20 inches of the rear exhaust vent or side intakes.
HEADS UP: In high humidity, it will fill up faster. For continuous drainage, you can attach a standard garden hose (not provided) to the drain port and run it to a floor drain, but the unit must be level or slightly tilted back for this to work.