selection saveinto

What are you trying to achieve here? Single selection or multiple?

single row selection

What exactly you want to do it in the selection save into. like you are using lot functions reverse index etc.

Grid selection works with multiple values. To limit it to one, there is no direct way and you have to manipulate the value in your code. Try the below code in your saveInto

saveInto: {
    local!value,
    a!save(
        local!value,
        index(local!value, length(local!value), {})
      )
    }

docs.appian.com/.../recipe-limit-rows-to-one.html

This technique works for me.  In fact I'm a little surprised I never thought of using "reverse()" before, since that seems a bit more efficient than the "length(save!value)" method I used in the past.  Can you verify that your individual gridRowLayouts have valid "id" values?

a!gridLayout(
  headerCells: {
    a!gridLayoutHeaderCell(label: "label")
  },
  selectable: true(),
  selectionValue: ri!selection,
  selectionStyle: "ROW_HIGHLIGHT",
  selectionSaveInto: {
    a!save(
      ri!selection,
      index(reverse(save!value), 1, null())
    )
  },
  rows: {
    a!gridRowLayout(
      id: 1,
      contents: { a!richTextDisplayField(value: "dummy row 1") }
    ),
    a!gridRowLayout(
      id: 2,
      contents: { a!richTextDisplayField(value: "dummy row 2") }
    )
  }
)

it's a method useful for storing only the most recent row selection AS the selection value - used for a long time now - as far as I can tell it should work, to be honest.

You can use local variable instead of using save!value