So I was playing in my world, and had a bunch of foxes and a horse tied to fences. I went to nether portal and my mobs weren't there when I came back, so I thought it must be MCPE-21416 .
After a while I attached couple of goats near the same place temporarily and after some time the goats weren't there too. I didn't go to nether this time and multiplayer toggle was turned off. Here are the fences from where mobs disappeared and chunk boundaries are marked with redstone dust.