PaperMC/paper-server/nms-patches/net/minecraft/world/entity/monster/EntitySkeleton.patch

--- a/net/minecraft/world/entity/monster/EntitySkeleton.java
+++ b/net/minecraft/world/entity/monster/EntitySkeleton.java
@@ -90,7 +90,7 @@
     }
 
     protected void doFreezeConversion() {
-        this.convertTo(EntityTypes.STRAY, true);
+        this.convertTo(EntityTypes.STRAY, true, org.bukkit.event.entity.EntityTransformEvent.TransformReason.FROZEN, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.FROZEN); // CraftBukkit - add spawn and transform reasons
         if (!this.isSilent()) {
             this.level.levelEvent((EntityHuman) null, 1048, this.blockPosition(), 0);
         }