Attempting to generate a Buffet style world on snapshot 20w06a with the settings Floating Islands and Soul Sand Valley selected will cause the game to freeze and stop responding a few seconds into generating it. As far as I can tell, there is no way to close the game from this state other than using an external program like Task Manager.
Environment
Java: 1.8.0_51 64 bit
Allocated Memory: 1664MB
OS: Windows 10 Pro
Duplicate of MC-171020 - please search before reporting