Why do young chickens continue to be paralyzed?

Recently, the paralysis rate of pink shell laying hens which are often encountered at the age of 50 Mel and 100 days is about 1%. Some technicians said it was Malik after reading it, but after dissection, there was no swelling of the sciatic nerve and no tumor, and even if the same batch of brown-shell layers did not have only pink-shell chickens, what was the reason? I hope all the experts will give us some advice.