I can't get it to load either. I've nuked local storage and it still won't load.
Discussion
The CORS errors are just failures to fetch Nip05 IDs from sites that won't accept requests from a web app. You can ignore those.
The likely reason you can't access NostrGram is because it's running off a web socket server on port 444. If you have a custom configured firewall it won't allow the request. Check your firewall and see if that port is open. On standard Windows/Mac/phone firewalls it is, but more advanced users might have more advanced lock-downs.