IMO it’s the different way to resolve a name from the OS and PHP.
Try:
echo gethostbyname("host.name.tld");
and
var_export (dns_get_record ( "host.name.tld") );
or
$dns=array("8.8.8.8","8.8.4.4");
var_export (dns_get_record ( "host.name.tld" , DNS_ALL , $dns ));
You should found some DNS/resolver error.