Why did an active torrent suddenly disappear?
The main reasons for this are: 1. The torrent may have been out-of-sync with the site rules. 2. The torrent was not seeded. Torrents expire after 5 days without a seed. 3. It was a bad release. A replacement will probably be uploaded to take its place. 4. The torrent expired. Older torrents are sometimes automatically deleted when the peer count gets high to avoid running out of RAM and killing the server.
There may be three reasons for this: #1. The torrent may have been out-of-sync with the site rules. #2. The uploader may have deleted it because it was a bad release. A replacement will probably be uploaded to take its place. #3. Torrents are automatically deleted after a scheduled period of inactivity.