I updated my Laptop running Windows 10 to Minecraft Windows 10 edition version 1.0.5, and upon opening Minecraft, I found all of my worlds, my skin, world templates, and username were gone.
I then updated other Windows 10 systems after backing up worlds, and none of the other systems had data erased.
I made sure to check the worlds folder, and restarted my computer. All of my data is gone.
I don't know what caused my data to disappear, but as I haven't messed with any of Minecraft's files recently, I can confidently say I didn't accidently erase them myself.
Hopefully this helps.
-MrPiedPiper

Edit: I don't know if this makes any difference, but upon turning on Minecraft after updating, I signed back into my X-box Live account, then went to my worlds list.