Custom Webpack Loader Breaks on Reload

Question

I have a very simple webpack loader that transforms a csv file (that has already been parsed by csv-loader) and processes any markdown in the csv's description field:

var md = require("markdown-it")()

module.exports = function (csvData) {
    let newCSVdata = eval(csvData)
        .map(x => ({...x, Description: md.renderInline(x.Description)}))
    return `export default ${JSON.stringify(newCSVdata)}`
}

When I start the simple project, with webpack serve the resource is properly built. However, if I make any changes to the CSV and save them, webpack immediately fails and I get:

ERROR in ./data.csv
Module build failed (from ./markdown-loader.js):
LoaderRunnerError: Module '[PATH TO markdown-loader.js]' is not a loader (must have normal or pitch function)

Stopping webpack and restarting it causes the problem to resolve and the csv is properly processed again.

Here is the webpack config:

const path = require('path');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'main.js',
    path: path.resolve(__dirname, 'dist'),
  },
  mode: "production",

  devServer: {
    static: {
      directory: path.join(__dirname, 'dist'),
    },
    compress: true,
    port: 9000,
  },

  module: {
    rules: [
      {
        test: /\.csv$/,
        use: [
        { loader: path.resolve("./markdown-loader.js") },
        {
          loader: 'csv-loader',
          options: {
            dynamicTyping: true,
            header: true,
            skipEmptyLines: true
          }
        }
        ]
      }
    ]
  }
};

Is there something special that needs to be done to the loader to ensure it works when the resource is reloaded?