On my SMP server I have realized a bug that seems to have been discovered back in 1.7 when chicken jockeys were added, and now it's back in 1.17. Much like the zombies picking up glow ink sacs that was fixed in 1.17.1, this one involves a chicken jockey spawning inside an unlit cave in a highly visited area that has been loaded for a long time and when the baby zombie despawns the chicken is set free to lay eggs all over the cave. These eggs are then picked up by zombies roaming around the cave making them permanent. They keep growing up to a point that affects server performance and in some severe cases server crashes. please look into it.