I traveled from the nether to the overworld, I waited like 5 minuts and I was still in the loading terrain screen from the netherportal, I then tried closing the game but it didn't work because my mouse pointer was looked on to my characters head movment(first person view). I shut down my device (Windows PC) and when I looged back into Minecraft, the world was gone, it is still in the world files of my pc but I can't access it anymore because it won't show up in the choose world menu, no mater how many times I restarted Minecraft, thank god I had a backup of the world. This also happened to me when I played a world back in version 1.13.2 The same thing, shut down device while in the loading screen of the netherportal and the world was gone.