Was the Dynamo outage separate? My take was the NLB issue was the root cause and Dynamo was a symptom which they flipped some internal switches to mitigate the impact to that dependency

If their internal NLB monitoring can delete the A record for dynamodb that seems like a weird dependency (like, i can imagine the nlb going missing entirely can cause it to clean up via some weird orchestration, but this didn't sound like that).

I was thinking more along the lines of the NLB being in front of DNS servers and dropping resolvers

Or an NLB could also be load balancing by managing DNS records--it's not really clear what a NLB means in this context

Or there was an overload condition because of the NLB malfunctioning that caused UDP traffic to get dropped

Obviously a lot of reading between the lines is required without a detailed RCA--hopefully they release more info