Wasn’t sure where to report this. Perhaps it was planned this way, but if so it would be unusual.
www.grin-forum.org resolves to an IP address through the nameserver associated with the domain, however grin-forum.org (no www) does not resolve. So usually an A record is supposed to be there, and a CNAME record for the “www” subdomain (technically it’s a subdomain). Below is a screenshot of nslookup. I used CloudFlare and Google’s DNS servers to confirm it was not just a DNS issue.