When Ores try to generate in lush caves then can overwrite already generated water pools which doesn't seem like intended behaviour (MC-219200 might affect reproducing this)

Seed: -240861352427657586 (Large Biomes)
/execute in minecraft:overworld run tp @s 784.42 57.74 872.43 -2645.95 50.85
Note: To create a large biome world you need to create it in 1.17 first then upgrade it in 21w39a