Torrents having trouble re-seeding

[brophy62]

I recently switched computers and needed to re-seed countless torrents on my new computer. I understand the process - add torrent > force re-check > start. However, there are still a number of torrents which when force-rechecked, will get anywhere from 0-100%. Any torrents above 80% I generally re-downloaded the remaining portion. However, many are at 0%-15%. I will not re-download these, of course. What could be preventing them from working? The folders check out correctly, I have not renamed any folders/files. I have definitely changed "tags" (if that's what you call them) in iTunes. But I have done this to almost all files in some way in iTunes, and some of them have worked nevertheless. What could be causing this? And what can I do to get these stubborn torrents seeding again?

Thanks!