hey micanushi.
Wonder if there’s an issue with the central control unit dispenser circuit pins or harness that’s compromising dispensing signal during the wash cycle? Have you done a visual inspection or tested continuity on the CCU?
Also, found an ''outstanding'' service manual for your model that you can download in pdf.
https://www.applianceblog.com/manuals/DuetWasher.pdf
Good Luck & please keep us updated.