How to use BIP39 test vectors?
You must add 'TREZOR' to your second line:

const seed = Bip39.mnemonicToSeed(MNEMONIC, 'TREZOR');

Then it should work.

You can see this in the BIP39 test cases in the BitcoinJS repo:

https://github.com/bitcoinjs/bip39/blob/4fce199e73f7ab68bdf9f7382dc10f7e1adaa499/test/index.js#L13-L33

function testVector (description, wordlist, password, v, i) {
  var ventropy = v[0]
  var vmnemonic = v[1]
  var vseedHex = v[2]

  test('for ' + description + '(' + i + '), ' + ventropy, function (t) {
    t.plan(5)

    t.equal(bip39.mnemonicToEntropy(vmnemonic, wordlist), ventropy, 'mnemonicToEntropy returns ' + ventropy.slice(0, 40) + '...')
    t.equal(bip39.mnemonicToSeedHex(vmnemonic, password), vseedHex, 'mnemonicToSeedHex returns ' + vseedHex.slice(0, 40) + '...')
    t.equal(bip39.entropyToMnemonic(ventropy, wordlist), vmnemonic, 'entropyToMnemonic returns ' + vmnemonic.slice(0, 40) + '...')

    function rng () { return Buffer.from(ventropy, 'hex') }
    t.equal(bip39.generateMnemonic(undefined, rng, wordlist), vmnemonic, 'generateMnemonic returns RNG entropy unmodified')
    t.equal(bip39.validateMnemonic(vmnemonic, wordlist), true, 'validateMnemonic returns true')
  })
}

vectors.english.forEach(function (v, i) { testVector('English', undefined, 'TREZOR', v, i) })
vectors.japanese.forEach(function (v, i) { testVector('Japanese', WORDLISTS.japanese, '㍍ガバヴァぱばぐゞちぢ十人十色', v, i) })
vectors.custom.forEach(function (v, i) { testVector('Custom', WORDLISTS.custom, undefined, v, i) })