I had a similar problem with 'dnscache' from the TinyDNS suite of tools a couple years back. Certain DNS names hosted in AWS Route53 would exceed the max number of requests to be resolved at random, because Route53 randomized the NS records it gave for each subdomain, so every once in awhile during the dns 'walk' dnscache would have to resolve their .net, .
co.uk, .org, and .com NS records, which blows up the number of resolutions pretty quickly. Akamai has the same problem. The internet was much simpler 20 years ago :\.
David