I've had many AWS support engineers (and higher engineers) look at things in our env and say "I've never seen that before" and have no clue what was happening. It's a two way street. Everybody can't know everything. And remember that many devs in the real world have much broader domains than AWS engineers - I have to know every nuance about 30 AWS services, as well as my own applications and my own domain. An AWS engineer would be limited to having a deep understanding of one or a few services, and has internal experts on individual services to reach out to when they don't have some information. But sometimes even AWS devs might not be aware of a little line in the Lambda docs like "Background processes or callbacks that were initiated by your Lambda function and did not complete when the function ended resume if Lambda reuses the execution environment. Make sure that any background processes or callbacks in your code are complete before the code exits." [1] There are gotchas like this with every service, and missing a single line within the novella of docs AWS provides for each service is not a significant failing. There are also issues and concerns that are completely undocumented and are only learned with experience.
As a developer for a SaaS, I have to spend some time on support every day, including for devs who have refused to read our documentation for a particular service we provide (and the only one these devs use). It's frustrating, I know. You should assume that the developers who are your customers are unlikely to be stupid, and are instead just not informed about something or haven't read the docs (maybe they didn't know where to look, or like many, they are too busy to justify spending a day reading the docs for lambda). Best thing to do is direct them to the relevant parts of the documentation and do your best to help those people.
