Why most of the time hacker news shows "Unknown or expired link" error?

I agree, it's the worst part I hate about HN...especially if you are deep down on page 10+ and it shows this "unknown or expired link". Now even if you startover you have sift through 10 pages to get to where you were. Annoying but as samwillis said it's the nature of arc I guess. I sincerely hope there are some workarounds to this.

This has been discussed many times: http://www.hnsearch.com/search#request/all&q=%22Unknown+...

Its due to the architecture of the listing pages, the more link is a closure on the server so that the order is preserved when clicking through the pages. It prevents you from missing an item that say jumps from page 2 to 1 as you navigate from page 1 to 2.

There will be a far better explanation from someone more educated in arc (the dialect of lisp HN is built in) and the general architecture of the site than me somewhere in the search results link above.

Everything, and I mean EVERYTHING, on HN revolves around these expiring id's. if you want to up vote a comment, the ID must be attached to the command. Next page, new comment, everything. It's a real bitch (especially since I'm integrating with it from an iOS app)

I think the "Unknown or expired link" error page should be a detailed explanation of the issue. If it will never be fixed, maybe we could at least get people to stop asking about it.

The worst is when you spend time typing in a post and it gives this errors on submission. Although one can back-tab, copy, refresh, paste and resubmit.

I believe it happens when you keep your session open for a long time.