Passive mobs will despawn randomly in Survival. I have only observed it in Villagers and Cows but I think it affects other passive mobs too. It may only occur in Survival but I'm not sure. To replicate: Spawn Villager or Cow, then change to survival. Remember where they are or keep them locked in a container or something similar. Then go off quite far away, maybe 100-200 blocks for about 10-20 mins and you will find some or all the mobs have despawned.
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[Mod] OcelotOnesie
migrated
Thank you for your report!
We're already tracking this issue at MCPE-21416, so I will resolve and link 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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