It does matter, because you asked what it could’ve been...
I know it’s frustrating when you think you’ve made a safe space, and something still manages to get your chickens. Everyone here was just brainstorming with you to help you prevent another death. I’m sure that no one meant to upset you.
Let’s start over.... the picture definitely helps, but can you clarify if the chicken body was found inside the enclosure, or outside? I think Patriot took your statement of “no chicken inside” to mean “no, [the] chicken [was] inside”. I know that I read it that way. Is that what you meant?
What Patriot was suggesting was that if a snake got in the enclosure, it would’ve found itself trapped by a bulge in its gullet after swallowing the chicken whole. After feeding, a snake gets slow and vulnerable, and if the other chickens were flapping around, freaking out about it being there, it would’ve felt threatened.... since it couldn’t escape with the chicken still inside, it would have regurgitated the bird, whole, so that it could get away. The bird would’ve looked just like what you showed, since snakes don’t chew or rip anything when they eat it.
A possible solution that would allow you to keep the youngsters in their own space would be to install 1/4 inch wire mesh on the bottom and sides of the cage. I’m not sure what kind of netting you were using, but if it could be pushed aside even slightly, there may have been a gap large enough for a snake to get in. You can still leave the netting on most of the cage, but overlap a few inches of the wire mesh over top of the netting, that way it can’t be moved to create a gap.
Of course, this same strategy will help deter any other predators as well.
I’m sorry for your loss. Good luck going forward.