I'm certainly no expert, I simply pass on my observations. I have been catching, studying, and breeding snakes for nearly 50 yrs and only had chickens for the last 19 yrs. Is it possible that your hens were trying to protect their coop and were pecking the snakes? If so, I would expect the snake to defend itself.
No, the hens were on roost well after dark. I heard a commotion and went to check, thinking a fox or coon had somehow gotten into their enclosure. Found the snake still actively constricting the hen.