Mobs (animals) randomly despawning

Well I know they are supposed to if they are not fed they are supposed to despawn when on leads, feed them so it dosesn't happen again

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We're actually already tracking this issue at MCPE-21416, so we will resolve and link this ticket as a duplicate.

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Reopening as this is likely to be a separate issue to the chunk border despawning issue.

Our horses, sheep (all named with name tag), mule, llamas, pandas, parrots, foxes, cows, pigs, chickens, cats, dogs, and fish have all disappeared.  Cows and sheep were the first ones gone.  Xbox one x, 1.13.0.1.  

My call log was merged with this one (MCPE-48125 Bucket Placed Fish Despawn from Aquarium), where I reported missing fish in an aquarium, I should add that now all my horses (with their saddles) and panda have disappeared, and the fish I placed back in the empty aquarium disappear after logging out and back into the game.

This issue is happening in my world too. I had 10+ Llamas, sheep, and chickens in a fenced in area. It was not on a border chunk. I interacted with the llamas everyday and they also had been given name tags. The sheep and chickens were bred as well as fed. I had two turtles in an enclosed area, bred them, and they still despawned after 30 minutes or so. It is becoming frustrating because I could spend hours looking for a specific mob, just for it to despawn right after I interact with it.

I had to get bunnies and foxes from other biomes, travel through the nether to bring them home, and they despawned! My sea turtle farm was also empty. My horses, cows, pigs, sheep, and chickens also disappeared within 2 hours of playing the beta (bedrock). Help!!!! 

So, per the other comments I have seen where people were saying to regularly feed the animals to prevent despawning - I did just that! I went around last night and caught new animals. I fed and bred them. I was feeling like maybe this would be the trick. NOPE! My poor animals de-spawned again!!! I do have a big stretch of land, but I keep most of the animals relatively close. It seems when I walk to the opposite end of my neighborhood, the animals on the other side disappear. 

@unknown: Disappearing is not necessarily despawning. In Bedrock, entities (all mobs and floating items and certain kinds of blocks) stop being rendered beyond about 70 blocks from the player. Moving back within range will cause them to resume being visible. This sounds like what you're describing in the last sentence.

But they are gone. 

I've been playing minecraft for like 8 years. I know how the rendering works. I'm saying that when I go away from my animals, I come back to empty pins. They have just vaporized or something. It only started when I joined the beta.

Multiple similar issues and mojang keeps closing them, 

https://bugs.mojang.com/browse/MCPE-50539

If you look at the related tickets (linked in the details above) there is another ticket regarding mobs despawning generally: MCPE-21416

The issue we had with mobs despawning in the early 1.13 betas was a separate issue, and has now been fixed.

For any ongoing general despawning issues, please refer to MCPE-21416.

Villagers are despawning when name tagged and so are animals that are name tagged on my realm!