This happened in older versions in MCPE as well. Leaving a chunk containing an animal on a lead tied to a fence post and returning results in the lead breaking and animal wanders free. Often, I can witness the animals and mobs "bouncing/ teleporting" from one spot to another
, Sometimes up to 30 blocks away when entering the chunk whether they're on a lead or not. I think this has something to do with lead breaking.
This doesn't happen every time, so please be patient. To reproduce, lead at least 2 passive animals to a fence post. Leave and allow chunk to unload. Return and one of the animals come off the lead, lead should be lying on the ground up to 30 blocks away from fence post.