The next best alternative would be BiglyBT’s Swarm Merging feature (which works similarly, and amazingly well on v1 torrents considering it only stores a precise file size instead of a hash in Vuze/Bigly’s own DHT). I’ve been able to ‘complete’ numerous separate torrents where availability was <1.
BiglyBT already supports v2 but dunno if Swarm Merging works with such torrents yet.
Actually, ufw has its own separate issue you may need to deal with. (Or bind ports to localhost/127.0.0.1 as others have stated.)