Washer does not drain even though coin trap is clean

Question

My Kenmore Washer (Model 11042926200) does not drain even though the coin trap is clear/clean.

Brief history: In the past, it frequently showed "Sud" and/or the error code "F02". After a few attempts/runs, things always started working again.

Today, these messages kept popping up and the door remained locked. I realized that the drain hose is bone dry. I had no choice but to manually drain everything and retry "Start"/"Drain"/"Cancel", followed by manual drains many times until the door would unlock. In total, I drained over 5 buckets of water via the coin trap (needless to say, everything is flooded) and the drain hose remained dry; no water came out there.

What concerns me is that the coin trap is clear and clean. There is also no blockage that I could see. This is how it looks like:

I am not sure if it's related but the first time I opened the coin trap, I found this piece of plastic stub/hose in the trap:

Can this be identified as a piece of a part?

How do I go about troubleshooting this?

Since I could drain all the water via the coin trap, is it reasonable to assume that the problem is downstream, not upstream? Downstream I would see only what I think is a pump (right of the coin trap opening).

EDIT: I meanwhile removed the two hoses from the coin teap/pump assembly and removed it. There is a clear path through this assembly. I also removed the drain hose. While there is some bit of residual in the hose, there is no clog, the water can run freely. Can the pump be broken? Is there a way to test this?

Answer 1

Writing my own answer after lots of learning: There is a small tube behind the drum that goes up to a sensor. Whenever the sensor senses water, error code Sud or F02 may appear.

Behind the pump and coin trap are two more pipes: One to the drain and one to the drum. Remove the pipes and clean.

The pipe to the drum includes a ball that floats and cuts of water flow if the draining is too slow. In my case, small fabric got stuck in there and probably forcing the float to go up and cutting the water flow.