nms.world.addEntity calculates 'i' and 'j', the chunk coordinates of the entity being added, before calling the appropriate create/spawn/launch event.

If the location of the entity is changed during the spawn event getChunkAt(i, j) may return the wrong chunk and the spawn will fail. If the new location is still within the pre-calculated chunk the spawn succeeds.

Simple fix is calculate i and j after the event has returned