This incident is now resolved, Amazon Route 53 DNS is now fully operational again.
10:24 PM PDT "Between 5:35 PM and 9:58 PM PDT, we experienced intermittent DNS resolution issues for certain specific AWS endpoints. We can confirm that DNS resolution issues for these AWS names have been resolved. Since DNS answers for some of these names that were affected by issues with the third-party DNS provider could have been cached on AWS DNS resolvers, we are flushing these resolver caches over the next few hours. If you run your own DNS Resolvers, and you experience DNS resolution issues we suggest to flush your DNS Resolver cache." - https://health.aws.amazon.com/