I still believe it is a timing issue. The collars have been known to slip on HD operators, I believe you probably have an HD 03 or HD 04. I used to set my gate on the hairy side of just making up, then bump it a tiny bit more so service geeks wouldn't yell at me for nuisance calls. DCL was done by closing door onto the stop, setting it, opening the doors a cpl inches, then using the manual door close button on the UDC til I saw the LED light on the board for DCL, verify no more door movement in the close. 1/4 gap between main dove tail of the clutch and pickup roller gave just enough clearance so the sequence of events could occur, and the CPU had time to see everything.

When I was reading the 2051 fault code, that's what I meant by it being indicative of a different problem. Had those collars slip more that once on me...still a little miffed on the redundancy fault, as I never had it happen to me. Perhaps the overall door scan has become muddled. I know if I move a limit or a parameter too much it's worth doing a quick learn travel just to make sure life is good.