Certain mobs not showing given names

Hi, I am having some trouble with names appearing above certain pets in the game. A few of my dogs and cats do not display their name above their head when I look at them (they are definitely named, as I got some friends to join the server and check and they confirmed they can see the name). I thought this might be for all mobs, but I checked some llamas and horses that I also tamed and their names show. I also checked some dogs that were tamed by my friend and the names on those show too.