Cannot transfer my old worlds to new Minecraft Better Together on XBOX ONE

i can´t transfer my worlds from Minecraft xbox One Edition to the new Minecraft (1.2.1) Better Together it says "syncronizing Minecraft data" and does not sync anything and sends me an error... Sometimes appears "0%" and then show me a sync error (( it only happen on Minecraft Better Together 1.2.1 Xbox ONE im from Mexico City, please fix it( i love my old worlds... greetings from Mexico...