At least one of your nameservers replied back without declaring itself authoritative. If none of your name servers respond with Authority, some services might fail if they are configured to only work with Authoritative DNS information and there is none to be found.
An Authoritative DNS Server means that it is the ultimate authority for reporting DNS Records for that domain.
As part of our DNS check, we request SOA records for your domain from each of your name servers. As we do so, each name server declares whether or not it is Authoritative, by setting or not setting the Authoritative Authority (AA) bit.
RFC 1034 describes what name servers are and defines what Authority means.
NAME SERVERS are server programs which hold information about
the domain tree's structure and set information. [...] Name servers
know the parts of the domain tree for which they have complete
information; a name server is said to be an AUTHORITY for
these parts of the name space. [RFC1034]
Having name servers which you intend to be Authoritative which reply without Authority can cause extra lookups when resolvers continue searching for an Authoritative answer.