If you didn't clear the platform code challenge, leveling didn't come into it.
We do respond to responses we get after rejecting people, but it can take us a few days; we tend to do batches of them all at once. My take is: while people are still in consideration, we have an obligation (we don't always meet) to be responsive, because people are pending their career decisions on our own decisions. Once we've communicated that decision, we're less obligated to be zippy, because you have the high-order bit of what you need from us.
I don't know anything about your submission and deliberately didn't try to look it up, because our grading of your work sample is nobody's business here, and I don't want to create the impression of communicating anything about it.
Having said that, I can tell you what we tell everyone who asks why their code sample didn't pass:
We've made a decision to budget the amount of time we ask from candidates, end to end, from application to final decision, to the amount of time they would spend in a hiring loop at a typical company that just did interviews and resume screens.
That implies that we have to keep our coding challenges short and succinct. I can't ask you to spend days coding something; that's more than an interview would ask of you.
A consequence of a short coding sample is that there's less surface area for us to derive signal from. We have to be pretty greedy about selecting coding decisions to judge, because there isn't all that much code to work from (for anybody who doesn't know, our current platform code challenge is to write a TCP proxy).
A consequence of having to jealously collect signal from coding challenges is that we're limited in what we can tell you about our grading. We can't offer you the rubric we use (there is one; reviews are mostly blind, and done by a pool of engineers), because that deprives us signal. We'd learn how good you are at following directions, but not much about how you approach systems programming problems.
I'd want a scoring rubric (and fast responses to emails!) too. I see where you're coming from. All I can do is tell you where we're at.