named and tamed foxes and ocelots despawn

I thought tamed foxes and ocelots wouldn't despawn, even with a name tag.

But they despawn after a few days even if I'm nearby. I keep them in a basement with grass and water and enough space to roam around

But after sometime when I check on them, they're gone. It's annoying to find new ones and waste nametags whenever they disappear. Especially with the white fox