DIAGNOSIS The smell is mold and mildew growing in hidden damp areas: primarily the rubber gasket/ring around the top of the drum (the "bellow") and in the dispenser drawer. Detergent and fabric softener residue traps moisture and feeds growth.
FIX First, run the proprietary "Clean Tub" cycle with LG's own washer cleaner (or liquid chlorine bleach) — NOT vinegar. While it runs, pull out the detergent dispenser drawer. Wash it in warm soapy water, scrubbing all compartments. Dry thoroughly. Wipe the entire rubber gasket around the drum opening with a 10% bleach solution, paying attention to the inner folds. Leave the lid open after every wash to let the tub dry completely.
IF THAT DIDN'T WORK If the smell persists, check the drain pump filter. A clogged filter can hold stagnant water. Locate the small access door on the front lower-left, place towels, open it, unscrew the cap slowly to drain residual water, and clean any debris from the filter.
HEADS UP Using more detergent than recommended is the top contributor. HE washers need very little. Excess soap doesn't rinse out, creating a sticky, smelly residue. Stick to one or two tablespoons max.