"Caves" or "Floating Islands" worlds from older versions (e.g. 1.16.5) will be corrupt in latest snapshot

Hi,

I think my bug report explains the floating island part, it is MC-306850 .

I did not do version hopping so maybe a dev can scheme in and verify.

Thank you for your report!
We're tracking this issue in MC-306850, so this ticket is being resolved and linked as a duplicate.

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