Similar problem here.
* Trying to access larger threads (70+ posts) will intermittently send me to the top of the last page oddly containing posts up to a year ago and none of the ones posted since then.
* Waiting a few minutes and reloading may then show posts up to several days ago, but the most recent ones still missing from the thread.
* Wait a few more minutes and reload, and the page may stay the same, revert to posts from a year ago again, or if lucky show everything properly and up to date.
* Within twenty minutes the thread returns to normal without problems. Then it messes up again several hours later, each time taking about 15-20 mins for the problem to disappear once more.
* During the error, post numbers are incorrect. What shows up as post #100 in the thread will later become post #88, for example, once the error goes away and all the newer posts reappear.
*(edit: the post numbers are off because some earlier posts duplicate themselves during the error - three or four of the same ones in a row, these disappear when the newer posts reappear. Weird indeed, perhaps a dimensional anomaly, haha. I'll roll back to 1.2.4 and see if that works.)
This started happening after I upgraded to 1.2.5 -- whether that is coincidental timing or related to 1.2.5 I'm not sure. The problem happens to guests, members, and administrators - although logging in sometimes corrects it.