FastStart

Can you elaborate a bit on what you're trying to do? Are you playing a game using FastStart and then it kicks you out when your download drops below 20 Mbps? I'm not sure what you're trying to accomplish, with a bit more information we might be able
to provide a solution, if there is one.

It's only for a set list of games right now, but I don't see a way to turn it off. Are you in the Insider program? That would definitely be feedback that needs to be seen.

Here is the FastStart info https://www.xbox.com/en-US/xbox-one/faststart

Here is where you can report issues like that https://reddit.com/r/xboxinsiders

Hi Gamer

I don't think there is an option to disable it

I also can't find anything related to Fast Start on Xbox Support

Hi Nate2572,

I don’t think your issue is with
FastStart as FastStart prioritises data so you can play whilst the game downloads. The only time it would effect or have negative impact would be if you are playing after reaching Ready to Start and your internet speed drops.

You may want to consider looking at the Network connection solution
page. I would say it is worth speaking to your ISP with regards to router settings as what if there are external factors stopping your Xbox from getting data from downloads and causing it to disable the download.

Do you get any error codes?

Fast Start brah

https://www.xbox.com/en-US/xbox-one/faststart