The game will sometimes despawn an entity and/or mobs if unloading and reloading the game while they are on chunk borders. This often will affect villages, barns, farms, and many other things whilst playing. If your game crashes this happens almost every time and I myself have lost all of my good villagers and their hard fought enchants to this bug. Please fix. Thank you.
Thank you for your report!
We're actually already tracking this issue at MCPE-21416, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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