We are getting F21 which is a drainage issue. This happened a few years ago and I pulled clothing out of the drain pump. fixed.
but now the drain pump is clear, but we still get F21.

I can feel what feels like a ball, or round object, right where the drain pipe connects to the tub. see images. Is this normal, or did a golf ball get stuck in there?!? Can someone squeeze that rubber gasket/hose right where it connects to the tub and see if they feel a round object. ?

First off Duet series are problematic but yes the ball is normal............Voltage test the drain pump while it's in drain mode if you get 120v to the drain pump more then likely the drain pump is clogged or bad.........Remove that clamp where the ball is and take a shop vac and vaccum out that whole area around your drain pump you can remove the ball while cleaning just put it back when your done and vaccum that whole entire line out all the wall to the where the hose goes in the wall also.............