[Experimental] - Super Flat World Chunks Being Deleted

When loading a superflat world from a previous beta that had caves and cliffs experimental features turned on, any previously created chunks have been deleted.

It appears that the old world has been shifted down 64 blocks into the void, which means the lower 64 blocks of the old world have just been deleted.
Update 1.17.40.21:

• While the world now loads old chunks, all block data hasn't been shifted down properly, all signs, chests, lecterns, etc. have lost their data.

Steps To Reproduce:

• Load any super flat world that had caves and cliffs turned on
• The world will have several deleted chunks

Expected Behaviour:

• Superflat worlds don't get deleted

Observed Results:

• Superflat world chunks from old betas get deleted