One of the anycasted DNS resolvers in Sydney Globalswitch gradually stopped responding around 15:10pm Sydney time. Approximately 25% of requests were not being serviced. Customers with both resolvers configured would have noticed delays for some DNS queries.
The issue was fixed around 16:00pm Sydney time.
We are not sure of the cause at this time, other than it would be related to a resolver software bug. We will investigate further and tweak our monitoring to pick up on this particular type of non-responsive situation