post disappearances

Why is that at various times in the afternoon, a whole bunch of topics in the Unread posts just disappear?
Almost 3PM US east coast time, the list just dropped to 1 page.

Do they get archived midnight Italy time or something?

That happens to me quite frequently. Logging off, unintentionally when the forum crashes, is the most common culprit. You can select the forum title, and see the unread topics. A real pain in the posterior, sometimes.