I've just installed a new Tuleap instance in version 16.5, and instantiated two projects using the agile cardwall.
I was able to modify the task tracker to display the assigned person directly in the card.
However, when I modify the assigned person directly from the cardwall, the change seems to take effect when I click OK, but if I do an F5 or return to the page, the changes are not persisted. I have the same problem when changing a task from column, after a refresh, its status change is not persisted and the card is located on the previous column.
Finally, for information, when I make changes directly from the task property dialog, the changes are taken into account.