IMO AWS once you get off the core services is full of beta services. S3, Dynamo, Lambda, ECS, etc are all solid. But there are a lot of services they have that have some big rough patches.
But yes, the less of a core building block the specific service is (or widely used internally in Amazon), the more likely you are to run into significant issues.
I'd add SQS to the solid category.
But yes, the less of a core building block the specific service is (or widely used internally in Amazon), the more likely you are to run into significant issues.