The thing is, the "more" links are specific to each user and generated page. They're not just "page 3 at the time you click on the link", but the actual next 30 links following the 30 it's previously shown you. As a result, it needs to store state for each of these links it's created (IIRC, the fnid is a reference to the closure containing that state). For obvious memory management purposes, these need to be expired after some time.

I agree that it's an odd implementation choice though. I guess it made sense when HN was smaller and it could grant more ressources to each user. Nowadays, Reddit's simpler system (with risks of duplicates or missing rising links as you go deeper) would probably make more sense.

I understand that it's a tough problem and can totally understand solving it by just making the links quit working like that. But that sort of thing doesn't strike me as "good", even if it is highly pragmatic.

And why not store that state on the client? 30 serialized ids is not that much.

Yeah, I really can't believe that hasn't been fixed by now.

Not only that, but it's impossible to follow discussions here. You have to go through your comment history to find threads you reply to.

The UI is in some way (i think) intentionally poor. For example, when you want to reply to a comment it takes you to a new page, and then you still have to click on the textarea to focus it. I think they don't want people to be able to comment quickly.