re: Another thread disappearing from 'postings in the last day'.
That's exactly what happened. When an earlier post is edited, the system looks at the original date and time of the post being edited, and that becomes the "latest date". If the edited post is older than the search parameter (such as "Last Day"), then it won't appear under that parameter. You can try the "Last Week" search to see if a "lost" thread reappears in the search.
Don't fear, the threads are not lost when this happens. They are still there.