Ok well your uploading at 6,000 kbps that's at 6 Mbps on your upstream to Twitch. That is a little high for that connection I prefer the 1/3 rule to allow for overhead with online gaming and other issues that may occur while streaming. So for your Scenario I would probably upstream at like 4,000 kbps at 1080p 24 fps. That's another rule of thumb I personally like to get into which is if your at a hard limit of your stream provider example Twitch has a hard limit of 6,000 kbps regardless of the resolution and frame rate for the general public. If you want higher quality streams you have to find providers that allow and offer that but a good quality upstream for 1080p at 60 fps is like 18,000 kbps at 30 fps and closer to 32,000 kbps at 60 fps when upstreaming meeting certain Quality benchmarks. Keep in mind at lossless quality or at max file size of 1 Farme at 1080p is roughly 6.5 Mb so if you have 24 frames that is 156 Mb at the max file size for one second of video at 2,073,600 px per frame.
I know this is a bit technical here but I hope this explains a bit more at what's happening more than likely at the hardware encoding level when you push the start stream button and how network limitations will prevent you from streaming at super quality or what I call our in house levels of recording.