Some weird stuff has been going on lately.
I've just looked at a thread with 11 posts - 11 posts = 2 pages. The first page displays, but when you try to go to page 2, it never shows. The eleventh post, so to speak, is there but it's not there.
I've also had situations where some people are seeing all the posts OK, and others are seeing some missing, or posts out of order. I have a feeling this is a cache issue.
As a very quick fix, I've changed the number of posts per page from 10 to 20.
If anybody notices anything funny happening, please post it in here and give me as much information as you can.