Losing Worlds when logging out after right dying in lava pls help me

.      I keep losing my Minecraft worlds after dying in lava and logging out after I die. I dont why this is happening I’ve updated minecraft (which was also a very buggy process) and I updated my xbox and this bugs still happens. I’ve currently lost 2 worlds to this bug and I’m not happy about it. When loading into the worlds the loading process stops at “Building Terrain” and it stops around what it looks like 85 percent. In summary Please help me I want these 2 worlds back. No