First pic show animals, second is when I started going away, Third is when I get back and they're gone.
I think this happen also to villagers.
So, if an animal/mob was in some place and when it's out of your sight and when you go back to the place the animal/mob is gone!
Thank you for your report!
However, this issue has been closed as Working as Intended.
These are the new despawning mechanics. You can read about them here.
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