Heroku | Cannot GET

I deployed an API to heroku. One of its functions is file uploading. I made a static folder called "uploads" and upload files using multer package.

app.use('/api/uploads', uploadRouter);
app.use('/uploads', express.static(path.join(__dirname, '/uploads')));

Above code snippet comes from server.js. Below is the router and multer setup.

    const storage = multer.diskStorage({
  destination(req, file, cb) {
    cb(null, 'uploads/');
  },
  filename(req, file, cb) {
    cb(null, `${Date.now()}.jpg`);
  },
});

const upload = multer({ storage });

uploadRouter.post('/', upload.single('image'), (req, res) => {
  res.send(`https://app.herokuapp.com/${req.file.path}`);
});


uploadRouter.post('/imgs', upload.array('images'), (req, res) => {
    try{
      let filesArray = [];
      req.files.forEach(file => {
        filesArray.push(`https://app.herokuapp.com/${file.path}`)
      })
      res.status(201).send(filesArray);
  }catch(error) {
      res.status(400).send(error.message);
  }

});

Something tells me that my approach is far from an ideal one. However, it used to work just perfect until I introduced multiple file upload. Now, images after being uploaded stay there for a little bit (I can access them via links like https://app.herokuapp.com/uploads/1623782012131.jpg) and disappear over few minutes. Then, these URLs throw the following:

Cannot GET /uploads/1623782012131.jpg

The thing is that my previous images that I uploaded before introducing multiple file upload are still accessible. I thought it had to do with heroku file size limitations but it was not the case since I've only used about 50mb out of 500mb. What might be the reason?