Axolotls keep disapearing

In a realm I have recently been playing on I found an Axolotl so I put it in a bucket and took it home. I put it in a aquarium and fed it then I went out adventuring, when I came home to check on my axolotl it was gone.

The next day I found a few more axolotls and brang them home, and put them in the some tank. I named them and bred them. But the next day when I logged on I found that some of them were missing. The ones remaining were the offspring of the ones that disapeered. I would also like to remind you that they were named, and this was on a realm.

Please fix this bug, if it is a bug.