I can't access some web site with curl command on several Ubuntu server in EC2

I wonder if some sites are blocking because of a lack of reverse DNS for the elastic IP? You might want to try this procedure, Create a reverse DNS record

When I changed elastic IP to other, I can access with curl. So, it looks an elastic IP has an issue... But I still don't understand root cause. My IP is not in IP black list. And I think usually web site doesn't stop access from normal IP address. So, I hope to support to find root cause.