Mobs entering a cauldron never leave the cauldron

In my plugin test world, I had this fairly random -hopper- CAULDRON somewhere, and chickens decided to enter it. They don't seem to be leaving it whatsoever, their AI isn't able to get them out.

I placed a grass block next to the cauldron to see if they would jump on it, that isn't the case.

How to reproduce: Put some chickens in a cauldron
Expected behaviour: Eventually, chickens will path track their way out of the cauldron
Actual behaviour: The chickens never leave the cauldron

See screenshot for my example
I couldn't really find related bugs.

I tested the behaviour for some other mobs.

Mobs that do get out of the cauldron:

• Rabbit

Mobs which also show the odd behaviour:

• Silverfish
• Creeper (Even if I'm in survival and tracked)
• Skeleton (Same)
• Zombie ()
• All other mobs that fit inside the cauldron (I also tested villagers), I guess.

I tested a zombie attacking a villager stuck in a cauldron, and it was not able to jump on top of the cauldron to get to the villager.