My Minecraft animals despawn in water when I'm not looking?

So, I raised a lot of animals on the mushroom island in Minecraft with mooshroom cows, pigs, sheep, chickens, and regular cows. I have another house on another place farther away. And one day, I decided to let all of my animals out except for two. I decided to go back to my other house and when I came back all of the animals that were in the water disappeared. This is happened before. Is it the water? It only happens when I leave and come back! I'm so confused. If someone could help, please answer!

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