Entity z killed by the game.

[Sarakatunga]

Hello, people of 7 days, I have a question about zombie entities. I see that when a period of time passes, for example 20 hours of the "Game" Any z entity or zombie dog is killed by the game itself. Does anyone know how I can do to avoid this? I want to make a zombie boss that has a lot of life but since the players take a long time to kill him since he is a "boss" the game ends up killing him. I tried putting another entity as an enemy animal, it works but sometimes the animation atrophies and gets stuck. There is no case right?