Ocelot despawning even when player is nearby

So I was looking for Ocelot in the jungle, I finally found one and put a lead on it, only for it to despawn right in front of me (I also lost the lead because of that) 

I did this multiple times and they kept despawning even if I was beside them and looking at them.

They don't seem to despawn like thatif you put a nametag on them. (This is my first post here so I don't know if it's possible to send a video that shows it)