Mob are despawning in the new dev builds

Hello, i found a critical issue about mobs in latest dev builds, looks like mob are despawning for some reason, i'm not exactly sure why but i found a way to reproduce it

1. create a skeleton mob
2. add him melee goal selector
3. make him equip an head on damaged
4. equip an armor with THORNS enchants on yourself
5. he will despawn when he gets damaged by the thorns enchant

Here is a video of the issue: https://www.youtube.com/watch?v=LhwRsXjmt58

Here is a full paste of the configs i used + error i get in console when this happens: https://paste.md-5.net/xiloruhadu.rb