Diagnosis
Recurring musty odor is caused by biofilm and mold in hidden areas the Clean cycle doesn't reach: the detergent dispenser drawer, the drain pump filter housing, and the rubber bellows folds.
How to Fix It
Execute a three-part cleaning protocol. 1. Remove the detergent drawer per instructions and wash it in hot, soapy water. Clean the cavity it slides into. 2. Wipe the entire interior of the rubber door seal with a 10:1 water:bleach solution, paying special attention to the bottom fold where water pools. 3. Run a Clean cycle with 2 cups of white vinegar (not bleach) placed directly in the drum.
If That Didn't Work
Mold may have grown inside the drain hose or the sump area. Clean the drain pump filter (located behind the small kick panel at bottom front). Inspect the drain hose for obstructions.
Heads Up
To prevent recurrence, leave the door and detergent drawer slightly ajar between washes to allow airflow and complete drying. Use high-efficiency (HE) detergent only, and do not overuse it.