Diagnosis
The Tub Clean cycle isn't enough. Mold and biofilm build up in the hidden parts—mainly the rubber door gasket (bellows) and the detergent dispenser drawer. The cold, efficient washes these machines use are perfect for growing funk if you don't stay on top of it.
How to Fix It
Wipe the entire interior of the rubber door gasket after every wash, especially the folded lip at the bottom where water pools. Pull out the detergent drawer and clean its compartment with hot water. Then, run the Tub Clean cycle with an actual washing machine cleaner (like Affresh or a cup of bleach) on the hottest setting, but without laundry in it. Leave the door and detergent drawer open after every wash to dry.
If That Didn't Work
Check the drain pump filter. If it's clogged, stagnant water sits in the system. Cleaning it (as per the OE error fix) can eliminate a hidden source of the smell.
Heads Up
Using too much detergent or fabric softener directly in the drum (instead of the dispenser) creates a residue that mold loves. Stick to HE detergent and use the recommended amount.