In the last weeks, quite a few people reported such problems with Twitch. Most of the time if they then try to stream to a different service, for example hitbox.tv, everything is just fine. You did not have dropped frames, so all packets you sent out, reached the twitch servers. From there on its on twitch to deliver it to your viewers without buffering.
What you can do is test a wired connection (wireless is not really recommended for streaming) and you could fix your late/duplicate frames by probably lowering your streaming settings a tad bit. For example downscaling the resolution slightly. And as mentioned, you can test streaming to hitbox and see if it buffers there as well.
Also, twitch can change every 5 minutes and when a LoL tournament starts, so another day and the results can be different.