Duplicate - https://bugs.mojang.com/browse/MC-170881
Because you were generating an ocean. It has tons of water, which made the error happen.
Can confirm 19w07a, Win 10. Seems to happen when generating chunks, generally water.
Ok, I looked and didn't see it. No problem.
They also spawn in very small areas. Which makes them not able to move at all (stuck).
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