When playing in Hardcore mode, if you die, you can pick the "Delete World" and "Spectate World" buttons.

If you pick "Delete World":
The game will send you to the main menu, the background image of the main menu will be a white screen instead of the village background. Then, picking Singleplayer, even though the world was supposed to be deleted, it will still be in the list.
After this you can:
-Pick any world;
-Delete the subject world;
-Restarting the game.

Picking a world will make minecraft freeze in a dark grey screen and you can't close it without task manager.

Deleting the subject world (or any world i guess), will put the background of that menu (which is that dirt block wall) to the last frame seen in that hardcore world (where you died).
But the effects of the main menu will continue.

Restarting the game is the only way to fix this and prevent these errors.

Picking the "Spectate World" button however will spectate the world in the players spawn point as usual, but the chunks around the spectator will take a lot to load. Only then you can leave the world and everything will be fine.