File permissions

But when I check the old file is still same although the file size corresponds to the new file.

You checked the file on the filesystem, or the file metadeta that is stored in Drupal's database?

If the file on the filesystem is showing the old contents but the new filesize, that seems ... impossible? How are you verifying the information? If it's by making an HTTP request for the file, it may be cached by your browser or some proxy cache.

I was just coming to update my issue to say that is browser cache related but you got to it before me :) Everything works as designed.

I still don't understand one thing though, why is it that on my local, the new file loads fine but for the other servers, I need a hard refresh on the file?

Other servers? If it's a browser cache issue, servers aren't involved - just the cache in each browser. Not sure I understand. But glad it's working out now!