The bug
Ocean monuments can generate in or extend to improper biomes after upgrading an old world.
To reproduce
Open the attached world
.
/execute in minecraft:overworld run tp @s 187.43 74.78 -371.38 267.75 36.15
Related issues
Attachments
Comments

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Relates to MC-237145.

We'll need a un-upgraded world download to look at this.

Attached a new world download.

Dupe of MC-239870