Grid only has one row

Hi guys, 

I think I am close to the solution, but I've been stuck with this for a while and figured asking cannot hurt.

I am creating an interface which is supposed to show the user data from another User Input Task and have them confirm it has been input correctly. For this I use a read-only grid which I configured according to the Appian tutorial. However, it displays the data in only one row, albeit separated in the pre-defined columns (so e.g. it will say for Underlying "Underlying1; Underlying 2" in one cell).

The data is pulled from a CDT as a rule input. It contains "flat" data like single booleans, but also arrays. For this exercise, only arrays are concerned. Do I have to manipulate the data beforehand or am I missing something major?

My code:

a!gridField(
  label: "Fixing Levels",
  labelPosition: "JUSTIFIED",
  data: ri!product_cdt,
  columns: {
    a!gridColumn(
      label: "Underlying",
      value: fv!row.underlying,
      align: "START",
      width: "AUTO"
    ),
    a!gridColumn(
      label: "Fixing Date",
      value: fv!row.fixingDate,
      align: "START",
      width: "AUTO"
    ),
    a!gridColumn(
      label: "Fixing Type",
      value: fv!row.fixingType,
      align: "START",
      width: "AUTO"
    ),
    a!gridColumn(
      label: "Fixing Level",
      value: fv!row.fixingLevel,
      align: "START",
      width: "AUTO"
    ),
    a!gridColumn(
      label: "Fixing Factor",
      value: fv!row.fixingFactor,
      align: "START",
      width: "AUTO"
    )
  }

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