Nodejs encrypt and decrypt using crypto decrypt badly only firsts characters

Question

I have a js script that crypt and decrypt a file using these two functions

Encryption

function encryptFile(fileName) {
    const input = fs.createReadStream(fileName);
    const output = fs.createWriteStream(fileName + '.crypt');

    var aes = crypto.createCipheriv(algorithm, Buffer.from(key), initVect);

    input
      .pipe(aes)
      .pipe(output)
      .on('finish', function () {
          console.log('FILE ENCRYPTED!');
      }).on('error', error => {
        console.log(error);
      });
}   

Decryption

function decryptFile(fileName) {
    const input = fs.createReadStream(fileName);
    const output = fs.createWriteStream(fileName + '.clear');

    const decipher = crypto.createDecipheriv(algorithm, Buffer.from(key), initVect);

    input
      .pipe(decipher)
      .pipe(output)
      .on('finish', () => {
          console.log('FILE DECRYPTED!');
      })
      .on('error', error => {
          console.log(error);
      });
}

Some assumption:

• I use aes-256-cbc as algorithm
• key is a 32 char string
• initVect is a crypto.randomBytes(16);

Using these two function to crypt and decrypt a file I obtain a bad decryption. No error while execution but when I open the decrypted file the firsts 9 characters is still encrypted. Indeed, if I insert at the begin of my file 9 random charachters, the whole content of my file was decrypted correctly but there are the firsts chars encrypted.
Any solution?

UPDATE
I also use these two function passing them the content of the file

Encryption

function encrypt(text) {
    const cipher = crypto.createCipheriv(algorithm, Buffer.from(key), initVect);
    let encrypted = cipher.update(text, 'utf8', 'base64')
    encrypted += cipher.final('base64');
    return encrypted;
};

Decryption

function decrypt(crypted_text) {
    const decipher = crypto.createDecipheriv(algorithm, Buffer.from(key), initVect);
    let decrypted = decipher.update(crypted_text, 'base64');
    decrypted += decipher.final();
    return decrypted;
}  

Using simple string these function work fine, saving the crypted (return of encrypt()) in a file, reading it and decrypt it the result decrypted (return of decrypt()) has the same problem.