I'm having these issues as well. It'd be nice if we could select the highest bitrate option without having to select "Auto." The player seems to regularly cycle through the various stream qualities and it's jarring. I don't tend to have issues with other streaming video things outside of gb's live stream player.
Everything now works as it should for me! It seems like it was something related to the insider build. I'm running the current stable release of windows 10, and while I don't normally do a clean install of windows to fix a text formatting issue on a website, I was very sick of dealing with other weirdness that running windows insider builds has caused!