Major domain routing issue

The issue you're facing with the redirect from the root domain (demo.com) to the www subdomain (www.demo.com) could be caused by a few different factors. First, it's important to ensure that the DNS configuration for the root domain is set up correctly, with the appropriate records pointing to the correct endpoint, such as the Amplify distribution URL or the origin server.

Next, you should double-check the custom domain settings in the Amplify Console, making sure the "Redirect from HTTP to HTTPS" and "Redirect from root domain to www subdomain" options are properly configured. Additionally, verify that the redirect rules in the "Routes and Redirects" section of the Amplify Console are correct, with the redirect from "demo.com" to "www.demo.com" using the appropriate 301 Permanent Redirect status code.

It's also possible that caching issues or the time needed for propagation of the changes (up to 24-48 hours) could be contributing to the problem. You should try clearing your browser cache and waiting a bit to see if that resolves the issue. Finally, ensure that there are no other conflicting redirects or configurations in other services that might be interfering with the Amplify-managed redirect.

If the issue persists after checking these potential causes, you may need to contact AWS Amplify support for further assistance, or consider alternative solutions, such as using a third-party DNS service or a custom web server configuration, to manage the domain redirects.