I have found something that is probably a bug but not as big as Herobrine but can possibly affect gameplay

I play Minecraft on different user worlds that only I play in one of my worlds I realised that a chicken was running near me then disappeared and the same with a horse they were still in the range you would see the animal so I realised this has to be a bug because I have neverseen anything like this happen in Minecraft I have played for a few years.