[MC-231919] Random blocks missing in a rectangle in cave.

In hardcore mode, found an unnatural generation of some type of cave. (Creeper explosion in the bottom).

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However, this issue is Invalid.

Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.

Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
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