Most of my mobs desprende including named and villagers

It started when I built a creeper farm, it took me some time and I got some cobblestone from a mountain with a house on it (my villager house). When I was done with the creeper farm I went back to check on the villagers. THEY WERE GONE! I thought I might have made a hole and a baby zombie went in, but when I checked there was no hole. I'm playing single player and nobody could have killed them. I was only 100 blocks away. Then I went to check my cows, THEY WERE ALSO GONE!! The pen was still locked so then I went to check on my sheep, all but 2 were gone! It was weird seeing 2 left. I had one more villager house 150 blocks away from the cows and other villagers and surprisingly they were not gone. But still it makes me sad all this hard work disappearing out of nothing. Some of the corn were even named. It all happened close to spawn so not far away from anything. I did experience a bit of lag since my iPad is old and the game like updated a bit right before. Please help!