Related to and basically the opposite of
In seed 8321433975529524506 at 80 30 -40 you'll find grass blocks that generate naturally in an underground pool. This should not occur.
It was not caused by enderman damage, and the world was generated in 21w19a.
MC-224494, the chunk loading order may play a role in whether you see this occur or not. When this occurred for me, I did not teleport myself there. I had my view distance at 10.