[Fizzlemizz]

MyFrame_Update is creating new FontStrings each scroll on top of the ones before.

Create the Fontstrings in CreateRow() so they only get created once

f.DKPInfo[i].Text1 = f.DKPInfo[i]:CreateFontString(nil, "OVERLAY");
...
f.DKPInfo[i].Text2 = f.DKPInfo[i]:CreateFontString(nil, "OVERLAY");
...
f.DKPInfo[i].Text3 = f.DKPInfo[i]:CreateFontString(nil, "OVERLAY");

In MyFrame_Update() just set the new text to the three FontString for that row

row.DKPInfo[1].Text1:SetText(...)
row.DKPInfo[1].Text2:SetText(...)
row.DKPInfo[1].Text3:SetText(...)

Create and Update would look more like

function CreateRow(parent, id) -- Create 3 buttons for each row in the list
    local f = CreateFrame("Button", "$parentLine"..id, parent)
    f.Strings = {}
    f:SetSize(core.TableWidth, core.TableHeight)
    f:SetHighlightTexture("Interface\\BUTTONS\\UI-Listbox-Highlight2.blp");
    f:SetScript("OnClick", OnClick)
    for i=1, 3 do
    	f.Strings[i] = f:CreateFontString(nil, "OVERLAY");
    	f.Strings[i]:SetFontObject("GameFontHighlight");
    	f.Strings[i]:SetTextColor(1, 1, 1, 1);
    end
    f.Strings[1]:SetPoint("LEFT")
    f.Strings[2]:SetPoint("CENTER")
    f.Strings[3]:SetPoint("RIGHT", -30, 0)
    return f
end
 
function MyFrame_Update(self)
    local numOptions = #TableData
    local index, row
    local offset = FauxScrollFrame_GetOffset(self)
    for i=1, core.TableNumrows do
        row = self.Rows[i]
        index = offset + i
        if (index == SelectedData) then
          row:SetNormalTexture("Interface\\BUTTONS\\UI-Listbox-Highlight2.blp")
        else
          row:SetNormalTexture(nil)
        end
        if TableData[index] then
            row.Strings[1]:SetText("Player"..TableData[index].player) 
            row.Strings[2]:SetText(classes[TableData[index].class])
            row.Strings[3]:SetText(TableData[index].dkp)
        else
            row:Hide()
        end
    end
    FauxScrollFrame_Update(self, numOptions, numrows, height)
end

I didn't put a lot of thought into positioning the FontStrings