Your web host may be blocking or rewriting them. Things to check:

• If the site uses Cloudflare: turn off Rocket Loader (Speed → Optimization → Content Optimization).
• In your hosting panel, turn off any JavaScript optimise / minify / combine / defer setting.
• Make sure the whole public/assets/js folder was uploaded.
• Then reload with Ctrl+Shift+R (or clear the browser cache on a phone).