Hardcore hearts change to normal hearts when closing hardcore world while in Nether or End

The bug

In a Hardcore world, if the player closes the world while being in the Nether or End, upon reopening the world normal hearts instead of Hardcore hearts are shown in the hotbar.

Reproduction steps

1. Create a Hardcore world with the Superflat preset

   minecraft:stone,minecraft:nether_portal;minecraft:plains;
   

2. Wait until you have been teleported to the Nether
3. Close the world
4. Reopen it
   Normal hearts are shown in the hotbar