Paper/nms-patches/MobSpawnerAbstract.patch

--- a/net/minecraft/server/MobSpawnerAbstract.java
+++ b/net/minecraft/server/MobSpawnerAbstract.java
@@ -95,7 +95,7 @@
                             ((EntityInsentient) entity).prepare(world.D(new BlockPosition(entity)), (GroupDataEntity) null);
                         }
 
-                        ChunkRegionLoader.a(entity, world);
+                        ChunkRegionLoader.a(entity, world, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER); // CraftBukkit
                         world.triggerEffect(2004, blockposition, 0);
                         if (entityinsentient != null) {
                             entityinsentient.doSpawnEffect();