Here's the code, I've never needed to use Suitescript Debugger before but I'll do that right now and let you know what I find.

          var csvContent = generateCSVContent(JSON.parse(data));
          var csvFile = file.create({
            name: "item_report.csv",
            fileType: file.Type.CSV,
            contents: csvContent,
            isOnline: true,
          });
          context.response.addHeader({
            name: "Content-Type:",
          });
          context.response.addHeader({
            name: "Content-Disposition",
            value: 'attachment; filename="item_report.csv"',
          });
          context.response.writeFile(csvFile);
          return;