Because the internet is made up of of countless internet providers, proxies, gateways, etc. there can be conditions where some of them have been configured to block content. While very rare, it’s possible for this issue to occur in ways that can block assets on your site - or anyone’s site.
If you have a subset of users that are not able to load your site’s JS or CSS assets it might be this issue. It’s useful to first report the issue to us via this thread. Because we don’t control those third-party systems we are unlikely to be able to resolve the issue but knowing the impact helps us understand and assess the impact of that third-party system. Then, one known step to mitigate is disabling Asset Optimization if your site uses it. Disabling and verifying might resolve this issue if their location was somehow blocked by this third-party.
If the assets are still not loading, please share your site details in the thread below and our team will help to debug further.