Hello,
I'm really little... After years of trust in Transmission I figured out, that some torrents don't connect with Transmission but with Free Download Manager they do. I want to inform the community about this issue. Configuration ist 10.9.5. Internal Firewall is on. Router Firewall is off. UPnP is on. The light in Network always shows red. If the internal Firewall is on or off dosn't matter. Some torrents connect without problems. But as I said... not all of them. Would be nice if Transmission would be the most reliable Client for Mac but for me it isn't anymore.