Axolotls despawning even when nametagged. ( I lost my blue axolotl )

So far 5 axolotls have despawned, even ones that I kept named after my real life pets that passed away. They are completely enclosed in a space with complete water source blocks with no openings, with no monsters able to come in because of light and outdoor security. I spent hours trying to get my blue axolotl which I know has an over 1/1000 chance of getting. Please fix this in a hotfix or something because I don't want to lose any more