I was an engineer that designed water treatment plants for 25 years and I’ve been a handyman for 10 years and this problem has stumped me for several years on my home machine (whirlpool duet front loader). I tried everything you might’ve read in this forum and every other. Of course the basics like unplugging it and clearing the error codes but all of the advanced stuff too . Replaced pressure transducers, drain pump, cleared all lines and filters checked circuit boards, leveled the unit check drain line configurations… no matter what it what I did it was always a temporary fix.
Then last week I got Covid and as I recovered I said enough is enough and I had the time to just tear the thing apart. Dissembled the whole drain system and you know what? the answer to this jumped out at me immediately. The internal drain line from the bottom of the unit to the top effluent line is the culprit. Right near where it connects to the bottom is a check valve. This check valve is supposed to stop that 2 feet of water that goes to the top of the unit for discharge from falling back into the bottom sump. It can fail and worse than that it was designed with a hole in it!! That’s right a rubber flapper check valve with a hole in it which is something I’ve never seen in my life. Even if it closes the water will very slowly trickle back in through that hole and eventually refill the bottom sump. The engineer that designed this piece of crap should be fired. Replace this line and you will be good to go (see link below) but I didn’t even bother. I just sealed the 1th inch diameter hole in the gasket and voilà. Cheers!
https://www.repairclinic.com/PartDetail/Drain-Hose/WPW10562025/3281119?TLSID=1779&Ref=611198&gclid=CjwKCAjwtcCVBhA0EiwAT1fY7-iTxN_gARWnH83_pboOw39X2uS0XFZBNdLLEHIuIAUGSQVRHOIyAhoCDc4QAvD_BwE