I don’t know the exact reason why it acts this way, note, but please understand that large offsets like what you’re requesting when you load these pages constitute a significant database load, and consider whether there’s a way you can replace some of this browsing with narrower searches, instead.
Basically, in order for the database to be able to grab results starting from 1000, it also needs to determine what the first 999 results would have been. Contrast the first page of submissions, where it only needs to grab the number of hits that will actually show on the page.
It’s quite possible that the error page you’re getting is related to this, either semi-intentionally or as a bug. The best thing you can do is open a Trouble Ticket (“Report a Problem” in the menu of the newer layout) under the “Report a Bug” category).
