Error: ENOENT: no such file or directory even when file exists in Firebase Cloud Functions

I'm relatively new to Cloud Functions and have been trying to solve this issue for a while. Essentially, the function I'm trying to write is called whenever there is a complete upload onto Firebase Cloud Storage. However, when the function runs, half the time, it runs to the following error:

The following error occured:  { Error: ENOENT: no such file or directory, open '/tmp/dataprocessing/thisisthefilethatiswritten.zip'
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: '/tmp/dataprocessing/thisisthefilethatiswritten.zip' }

Here's the code:

const functions = require('firebase-functions');
const admin = require('firebase-admin')
const inspect = require('util').inspect
const path = require('path');
const os = require('os');
const fs = require('fs-extra');

const firestore = admin.firestore()
const storage = admin.storage()

const runtimeOpts = {
    timeoutSeconds: 540,
    memory: '2GB'
  }

const uploadprocessing = functions.runWith(runtimeOpts).storage.object().onFinalize(async (object) => {
    const filePath = object.name
    const fileBucket = object.bucket
    const bucket_fileName = path.basename(filePath);
    const uid = bucket_fileName.match('.+?(?=_)')
    const original_filename = bucket_fileName.split('_').pop()

    const bucket = storage.bucket(fileBucket);
    const workingDir = path.join(os.tmpdir(), 'dataprocessing/');
    const tempFilePath = path.join(workingDir, original_filename);

    await fs.ensureDir(workingDir)

    await bucket.file(filePath).download({destination: tempFilePath})

    //this particular code block I included because I was worried that the file wasn't
    //being uploaded to the tmp directly, but the results of the function 
    //seems to confirm to me that the file does exist.

    await fs.ensureFile(tempFilePath)
        console.log('success!')
        fs.readdirSync(workingDir).forEach(file => {
            console.log('file found: ', file);
            });
        console.log('post success')
        fs.readdirSync('/tmp/dataprocessing').forEach(file => {
            console.log('tmp file found: ', file);
    })


    fs.readFile(tempFilePath, function (err, buffer) {
        if (!err) {
            //data processing comes here. Please note that half the time it never gets into this
            //loop as instead it goes into the else function below and outputs that error.
        }
        else {
            console.log("The following error occured: ", err);
        }
    })
    fs.unlinkSync(tempFilePath);
    return
})
module.exports = uploadprocessing;

I've been trying so many different things and the weird thing is that when I add code into the "if (!err)" (which doesn't actually run because of the err) it just arbitrarily starts working sometimes quite consistently, but then it stops working when I add different code. I would have assumed that the issue arises from the code that I added, but then the error comes up literally when I just change/add/remove comments as well... Which should technically have no effect on the function running...

Any thoughts? Thank you in advance!!! :)