As you can see the upload is low. I run the torrent on a second computer and my download was ~ 500 kbps, on normal torrents my download was 2-3 mbps. Files that I share are 1-10gb. Do I need a dedicated machine for this number of downloads?
I checked the seedbox on speedtest and upload was ~ 900 mbps, so I do not know why so little seed?
First of all a seedbox does not guarantee any kind of seeding. Your upload speed is depending on many factors including the leechers of the torrent (their count, their download speed, their torrent client), other seeders (their count, their upload speed and their torrent client), on your HDD / SSD load (for better performance you should use SSD, since it has way faster diskio), your upload speed (which you mentioned that is fine) and lastly your torrent client configuration.
I have seen users who have shared as 5x times more than others who carry the same time as seeds while others have shared as 20,40,9 gb, I suppose they all have seedbox, because they all end up downloading in 5min aprox, then, like A leecher completes a rise up to x5 times ?, I suppose it is by ping, or the geographic location of the seedbox .. or as it says @Macroco by the configurations, even so it is not clear
I've seen things like this before on TL where there are a lot of partial seeders. A partial seeder is someone who's configured their client to only download some files from within a torrent, but not all. When that happens it looks like there's a lot of peers in the torrent relative to the number of seeders, but nobody is downloading so you can't upload.
Check your peer list and see if there are a lot of people with most, but not all of the files who aren't downloading anything.