Piglin/hoglin become Persistant when within 16 blocks of a player, causing massive lag due to piling up entites
The bug
If a piglin or hoglin is within 16 blocks of a player, they get the PersistenceRequired:1b tag, making them unable to despawn and no longer count towards the mobcap, which results in thousands of mobs beeing alive in the nether and never despawning again.