This bug is in the same world as this bug report: MC-90559, where spider spawners spawn phantom skeletons with odd behaviors.

Zombie spawners will spawn zombies like normal until the area is lit up, then they will start to spawn chickens. The chickens act like they are being ridden by child zombies and will follow you and can inflict damage. They spawn about once every 5 seconds. They can spawn regardless of light level. Once a chicken was on fire, other times they've spawned in a wall and immediately suffocated. If you exit and reenter the game, 4-5 child zombies will have spawned (along with some more chickens). On peaceful mode, nothing will spawn. Getting rid of torches and letting zombies spawn normally again stops the issue.

To get this bug I edited the custom world options to have the maximum number of dungeons, starting playing as normal, and here we are.

Spider spawners also act weirdly. As mentioned in the other bug report. No word on other types of spawners.