Seems strange to do this since this value is part of record, but added this to my snippet and it works.

model.updateRow(row,'agf__Assignee__r.Name',AssignedToRule.getFirstRow().agf__Assignee_Assignment__r.Name);<br>

Seems in some way related to an issue I had where I was using model actions to populate a reference field and I couldn’t get the name to display and Rob pointed out that you have to first populate the Reference’s ID, then overwrite it with the name. Perhaps it is what is happening in your example?