I noticed the issue with a torrent for which I was the only seeder after it was made freeleech. Many clients would connect and they all would sit at zero percent without transferring data.

Deleting the old torrent and adding a new copy downloaded from gaytor.rent worked instantly.

After a user switches over to the new site, do we need to redownload torrents to keep seeding them?

I was seeing an issue where an old torrent would allow users to connect, but a data transfer would never start. Deleting the torrent and adding it from scratch did work, but I don't know if that's something I'll have to do with all my old torrents or if it was some weird corruption issue in my torrent client.

Would it maybe have something to do with the tracker host name changing? I've never seen it happen before with old torrents I was still seeding.