World's Dissapear and replaced by World created in "1970"

When loading up my main world, the game crashed and as I reloaded it the world had dissapeared. I scrolled through the list of worlds to see if it had been for some reason moved but I found a new world with a random string of characters for a name created on "1.1.1970". I'm not sure why this was there or why my world has dissapeared but this seems to be because of the new update.