Baby zombies that ride chickens are spawning not only invisible from zombie spawners but also when the light level is high enough to stop them from spawning.
MC-90069
Invisible baby zombies riding chickens from spawner
Resolved
Duplicate
0
Rhys O'shea
(Unassigned)
Unconfirmed
Minecraft 15w41b
Retrieved
Happening to me in a mob trap, too. I can hear the zombie groaning, and the chicken is running at me, but you can't see the zombie. Killing the chicken gets rid of the zombie too.