Arailian

Recently I started playing on an experimental world with the new terrain generation. We created an animal enclosure with 7 sheep, a chicken, and a cow. Besides that, we also locked up a villager (which we abducted from a village) who sold us mending. The villager was locked up with a number of fence gates and iron doors to get out. The area was brightly lit so no mobs could spawn. 

After a few in-game days, I noticed only 5 sheep and the cow remained in the animal enclosure. After another 2/3 in-game days, only 2 sheep remained, and the villager was also gone. While I know chunk borders are often at fault in cases like this I checked if the might be an accidental chunk border in the enclosure or villager cell. But both of those were in the center of a chunk. 

The fact that this happened so regularly (every 1 or 2 in-game days another one would disappear) made keeping animals/villagers impossible. Both the animal enclosure and the villager cell were within 50 blocks from my base and I did not travel to the nether or further than 100 blocks away from my base during the days the disappearances happened.

This is also happening to me. I have checked to see if it was due to the fact that I was wearing other items which have mending on them. But they did not influence the result. See video for evidence and explanation

This happend to me on a realm without any custom texture packs, see attached video