The game crashes when transferring a major world (on a flat world where the majority of the Xbox 360 portion is used) on old Xbox one edition world to the bedrock version

So I have a flat world that I made back in October 2012 on the Xbox 360 version when flat worlds and creative mode was added, it is the biggest world I have (majority of the Xbox 360 portion is used) then transferred it to the Xbox one version in October 2016, now here I am trying to transfer it to the bedrock version and once it hits 3% or 4%, the game completely crashes and sends me back to the Xbox home screen, and unlike some people who's worlds are over 100MB, my world is only 18.7MB despite the size of the world itselfand it still crashes, but when I transfer a world that's 30MB, it works perfectly, so I hope this gets fixed soon, I don't like it when my biggest world has issues. It did this in the beta and still does it in the full release. Still does it in 1.2.3, why is this not fixed yet?