Sounds like to me might be a cache problem, with your browswer. If you cleared cache it might help. Also, when it doesn't show, do you mean the whole page doesn't even load, or what?does it to me , what i do is go in to the thread lets say its 2 pages i go to the second page and hit reload and that works everytime. this has been goin on for me i would say 2-3 months.
If you click reload on page 4 after you click on 5 does page 5 show fine?I have had many issues with threads having lets say 5 pages. I'm on page 4, go to click on 5. It loads, and I'm still on 4. lol