Named axolotl despawned

Hello! 

 

I hope whoever is having a nice day.

I have a problem. I created an axolotl reserve in my world with enough water and land and I released one axolotl from my bucket to the reserve and I even named it to prevent it from being despawned however when I came back, it wasn't there anymore  there was no way the axolotl could've escaped since it was a semi closed area.