[edit: it must be early, I forgot to use the 'check for errors' option. The two latest messages have now appeared. Sorry :)]
I have one topic (http://www.baroeg.nl/forum/index.php?topic=1103.0) where the latest additions don't show up. New posts to that thread don't disappear completely, because they are visible in most recent posts (http://www.baroeg.nl/forum/index.php?action=recent), the reply page and the split topic page.
The forum is in Dutch, BTW. No important packages installed (only custom profile mod and a set of smileys)
I haven't found an answer as to why this happened - but to be honest, I didn't know where to look.