We had a similar problem in our last unit. All the sanitizing wouldn't cure it. Finally discovered the water in the washer prep lines was the source. Flushed and sanitized them and the smell went away.
Mike & Donna Ishler Ontario, NY KE2LU FN13
2010 3605RL XFactor TST S637's
2017 Dodge 3500 Laramie CTD 4x4 Auto