Helpless Victim doesn't spawn custom mobs on death

Okay so I've just discovered a new issue. I'm not sure if you guys have seen the post but someone else released a mob called a Helpless Victim. On death it spawns horsemen bosses that try to kill the player. It used to work but recently hasn't been spawning the horsemen on death. What have I done wrong and how can I fix it? Thank you!

Mobs File:
https://pastebin.com/YRrantHJ

Items File:
https://pastebin.com/ENShMPag

Drop Table File:...

Helpless Victim doesn't spawn custom mobs on death