Sometimes if OS is restarted, the Down- and Uploads don't go on until I pretend to download a new file from the friend (whose down-/uploads don't run).
With pretend I mean that I mark a Swarm he offers and click on download and OS starts loading the Swarm-Information. Doesn't matter, if I actually chose to really load the Swarm, checking it and a click on download is enough.
Regards Katana