Animals/Horses/Villagers/Any entity dissapearing

Animals and Horses (even leaded Entities) Mysteriously disappear after reloading a world (not every time). If the Entitie is leashed it disappears, only leaving the other end that's tied to the fence post. it's more common for leashed entities to disappear than ones in pens, and no holes are present in said pens. Villagers also tend to disappear often (sorry I don't have any photos or videos of this happening)