Cannot sync world on xbox one or windows 10 minecraft or realms

We started a world back last January and had it on pretty much 24/7 on the xbox one. around July ish the world stopped syncing and we couldn't get into it. it just timed out every time. before then if certain people joined it would just crash the world and kick everyone out and it would take us a good hour to get back into it. we thought it was an issue with the xbox one itself. but it happened on multiple xbox's.

now that realms is out we'd like to try again with the world. but unfortunately not even realms can sync it. we have no idea whats going on or how it could happen.

we have tried multiple xbox's and even windows 10 versions
we've deleted and reinstalled.
removed save games
tried hard boots
and even tried full factory resets on all machines and unfortunately the world just wont sync

xbox gamertag is UKGN Minecraft

if you can fix this world that would be amazing!