I had a problem with an ACME cert terraform module. It was doing the R53 to add the DNS TXT record for the ACME challenge and then querying the change status from R53.
R53 seems to use Dynamo to keep track of the syncing of the DNS across the name servers, because while the record was there and resolving, the change set was stuck in PENDING.
After DynamoDB came back up, R53's API started working.
the Billing part of the console in eu-west-2 was down though, presumably because that uses us-east-1 dynamodb, but route53 doesn't.