I think I've worked out why people sometimes follow links and end up on blank pages with all the page numbers showing but no posts. It has been brought up a couple of times in QSF since the upgrade.
Say User A has a preference of 25 posts per page. They link to the last page of a 200-reply thread, which in their case will be page 8. User B clicks their link with a preference of 40 posts per page, but for them, page 8 doesn't exist (their thread stops at page 5), so they get the blank page.
Is there any way you could fix this, or perhaps refer it up to Rick? It might be better, rather than specify precise page numbers, to specify the first post id you want to appear on a page. This would fix the problem.