Game Crash

So me and my friend(who is on Xbox) have a world and it has a bunch of houses in it and we ran far away to get some sand and when we came back every time we passed a certain line on the map our games crashed.. We tried going around and it still crashed. We went into the nether and it crashed when we tried to re enter the portal and sometimes when it crashed if we were on horses the horses would disappear and so did some things in our inventory