Massive lag with thousand of chicken spawned

I experienced a massive lag suddenly. The world cant be loaded properly, pressure plates dont work. But the most important is, i found thousand of chicken were spawned in my farm which maybe the main reason of the lag. I tried to kill them and it improved. But then it turned out to spawn villagers... Am i hacked or it's a bug to the spawning system?

I have no where i can turn to... so please help to have a look and crash report is attached.

What I expected to happen was...:
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What actually happened was...:
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Steps to Reproduce:
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