I am curious what exactly happens when you remove torrent from your channel. Would people still see this torrent in my channel if they had only discovered it and not subscribed?
People only see a small subset of torrents as a preview of your channel if they have not subscribed to your channel. This may not reflect the actual state of your channel. This is because the preview of the channel based on the remote search query asking your neighboring peers if they have this channel and can provide some content of that channel. If those peers don’t have the latest channel updates, the results you get will not be up-to-date. On the other hand, if you subscribe to a channel, it gets synchronized regularly with the owner’s channel.
why after subscribing some channels still have not finished ‘downloading’.
All subscribed channels should eventually finish downloading if there are sufficient peers seeding it. Seeders are the subscribers of the channel including the channel owner. If there are no subscribers available, downloading cannot complete.