When I die in a Hardcore world, and click 'delete world', I get taken to the main screen, except it's a white screen, instead of the minecraft world for the background, and the world doesn't get deleted.

Thank you for your report!
We're actually already tracking this issue in MC-30646, so I resolved and linked this ticket as a duplicate.

However, that ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in the latest development version of the game.

If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.

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