Generally, things like connection speed throttling (ISPs have been know to do this to certain services), packet loss, and various other factors will affect things like RTMP when it doesn't affect something like loading a webpage or a generic speedtest. Please understand that saying "I can upload a video to youtube" is 100% irrelevant to the issues you're having. Not only is it a completely different website, there's a completely different protocol being used for those types of connections. You need to call your ISP, explain the issue, and have them investigate. Explain EXACTLY what you trying to do, and the issue that you're having. They'll do all the generic line tests, and if they find nothing, ask them to explain to you why you can't stream to Twitch, as you're getting nearly 40% packetloss.