worldLoad

Restores the world reference and, when the boss already sits in a loaded chunk, spawns it straight away.

Only re-attaching the world is not enough. A boss whose world was unloaded is filed in com.magmaguy.elitemobs.mobconstructor.PersistentObjectHandler under the world name, and the handler only hands it back to chunk-based tracking here. Bukkit loads a world's spawn chunks inside Bukkit.createWorld - before WorldLoadEvent is dispatched - so the ChunkLoadEvent for those chunks has already fired by the time this runs. Without spawning here the boss waits forever for a chunk event that will never come again. WormholeEntry#worldLoad has always done this; custom bosses did not.