Connection limits could be one part of the story, im not sure what the defaults are in qBit but i have set mine at 100 or something like that. Another issue that you could be facing is the torrent itself, it might already have 100+ people with seedboxes seeding but only a few peers downloading, since so many people are alredy uploading its hard for you to get any upload in. Try a few other torrents, preferably once with only a few seeds but quite a lot more people trying to download.
I have been using ultra for over a year now and dont have the issue you are talking about. How many seeds/peers do the torrents have? Might just be that there arent a lot of people dling what you are seeding
