The result from dnschecker.org is 100% expected, because the name ns1.infinityfree.com is to be used as the NS record, it doesn’t have NS records itself because that’s not how nameservers work. If you want to check whether the nameserver exists, you should check whether it has an A record to point the nameserver name to the IP address of the actual nameserver itself. And if you do, you’ll see that it’s working perfectly.
Besides that, it sounds like another case of this error: