I am creating a file upload feature to upload multiple files(images) to the express application. I have configured the multer middleware with size limits and file mimetypes as follows :

const storage = multer.diskStorage({
    destination: function (req, file, cb) {
        cb(null, 'uploads/product_images/');
    },
    filename: function (req, file, cb) {
        cb(null, "product-" + Date.now() + '-' + uuidv4() + "-" + file.originalname);
    }
});

const upload = multer({
    storage: storage,
    limits: {
        fileSize: 1024 * 1024 * 5
    },
    fileFilter: function (req, file, cb) {
        if (file.mimetype === 'image/jpeg' || file.mimetype === 'image/png') {
            cb(null, true);
        } else {
            cb(new Error('Invalid file type, only JPEG and PNG are allowed!'));
        }
    }
}).array("images")

to handle the errors given by the cb in multer, I have created an error handler middleware which I have place after all productRoutes as follows :

const productRouter = express.Router();

productRouter
    .get('/', fetchProductsList)
    .get('/:product_id/:size', validateProductDB, fetchProductById)
    .post('/', isAuth, upload, validateProduct, handleValidationErrors, createProduct)
    .patch('/:id', upload, updateProduct)
    .delete('/:id', deleteProduct)
    .get('/colors', fetchColors)
    .get('/sizes', fetchSizes)
    .get('/genders', fetchGenders)

// Custom error handler for Multer errors
productRouter.use((err, req, res, next) => {
    if (err instanceof multer.MulterError) {
        // A Multer error occurred when uploading.
        console.log("message from multer instance : ", err.message)
        return res.status(400).json({ errors: [{ msg: err.message }] });
    } else if (err) {
        // An unknown error occurred when uploading.
        console.log("message not from multer instance : ", err.message)
        return res.status(400).json(err.message);
    }
    next();
});

I am not getting any response when I try to upload a file which is not an image and is greater than the size limit. But I get the error printed in the console from the custom error handler middleware.

Another fact : everything works fine in postman.

What is wrong with this code.
To check the full code go to this repo : https://github.com/ishanjarwal/mern-sneaker-store
Please explain the reason for the problem and possible solutions.