I had it a few times over the weekend on specific threads. Basically, the thread on the front page has the Replies/Views column and Last Post By column on the right. A thread I had been posting in would have data like "Replies: 289" and "Last Post at: 10:20 AM". When I clicked on the last page of the thread, the post at 10:20 AM would be the last one I would see.
But! I was getting notifications I was getting XP and being quoted in the thread. So when I clicked on the notification to see the post I was quoted in (because of my ego, of course), it would take me back to the thread, but I wouldn't see any post later than the 10:20 one, even though the notification said I was quoted at 11:00 AM. I could even click on the profile of the person who quoted me, go to "See Forum Posts", and I would see the post they had made. But when I clicked on the post, back to the thread, still no posts later than 10:20 AM. This went on for hours. I even made a post in the thread, which went through, but I couldn't see it or link to it. Changing the URL in the browser to go to a different, higher page also didn't work.
What eventually did work was changing the thread sort from "Oldest First" to "Newest First". Now I can see new posts, but reading the threads backwards is pretty annoying. I'm going to switch it back and see if I still have the problem.
Edit: Still happening. I switched the thread sort back to Linear - Oldest First, and checked the "Geniuses with 5 Int" thread in the 5e forum. I can't see any posts made past Saturday at 6:20 PM EDT, and I know there are a few more pages of posts since then.
To follow on with this using the same thread as an example:
Using Linear - Oldest First the last page shows for me (10 posts/page) as 35, with the last post being by pemerton at 7:19 PM EST on Sunday, 11 April. If I switch my view to Linear - Newest First, the last post is by me, today (Monday, 12 April) at 11:49PM EST). The 5e Forum home page shows the thread with the last post by column having my post as the last one (which is correct). In Linear - Newest First, I still see only 35 pages, and, when I go to the 'last' post I can, which should be the OP in Linear - Newest First, the post is not the OP, and is also numbered as post 0, not post 1.
None of these problems exist in Tapatalk, where I can view the whole thread. I haven't tried the mobile skin.
EDIT: Problem persists if I log out.
EDIT2: I burned down all of my cookies and history (it was time, anyway), and the problem persists. I tried without logging in at all, and then logged in, same conditions as above. The thread only shows 35 pages.
EDIT3: AHA! Well, not aha, more, ahhh. I changed the number of posts per page from forum default to 20, and got a slightly different indication. Now, instead of 35 pages in the thread (Geniuses with 5 INT), I see 18, and the last post is by BoldItalic on Monday (12 APR) at 6:35 AM EST. So, I picked up a few more visible posts, but it still cuts off the last few.
Also, for easy of finding:
The thread:
http://www.enworld.org/forum/showthread.php?482860-Geniuses-with-5-Int
The last post with Linear-Oldest First and 10 posts per page (post 350):
http://www.enworld.org/forum/showth...5-Int/page18&p=6871800&viewfull=1#post6871800
The last post with Linear-Oldest First and 20 posts per page (post 360):
http://www.enworld.org/forum/showth...5-Int/page18&p=6872255&viewfull=1#post6872255
Hope this helps troubleshoot.