Dissapearing mobs

Ok so basically, I died 2 times and have sheep, chickens and a villager in my base. I respawned and half of the sheep were completely gone, and so was the villager. The entities that didn't dissapear were persistant ones like my tamed wolf or iron golem, but the villager is completely gone. I think this must be a bug where when the player dies the game doesn't save the entities in the surrounding chunks and makes them despawn even though they are not supposed to. I also noticed this happened when my game crashed and I re-opened the app, certain sheep were gone and the villager was also gone. I had to get another villager and transport him all the way to my base just to have him de-spawn because of a dumb chunk entity saving glitch.