Me and my sister were playing on a creative world where we we had a big pond with our named dolphin in it, we also had some turtles and some tropical fish in our pond but they stayed put. I went to decorate a house that is on stilts above our dolphin pond, and my sister went to explore, when she came back all but one of our dolphins had despawned. We were confused as named things don't usually despawn. We did an experiment where we caged one named dolphin and one without a name, when we checked back after a little bit the named dolphin had vanished while the unnamed one stayed put.

What was supposed to happen???

our named dolphins should have stayed and not despawned