Not sure how a 20 HOCLS compares to say a 10 UCL (not sure i ever saw the other model) which i can relate to (not sure of the naming meaning for you) but can you clarify if a middle level stop occurs if "only" 1 car stop is pushed? I would check the crosshead for the actuation of CAC-DCS,1ACS-1DAS,2ACS-2DAS just to make sure that the selector is getting a stop signal to ST and S. You seem to be getting a hook circuit signal to energise XD, so that appears ok. So i would look around the relays S, ST contacts, flexs etc, and see how you go.