I was told to provide sand, or #1 grit, to my baby chicks by the "chicken lady" at our local farm store. So go figure. Also, the dust bath is full of sand. Fortunately, my birds are healthy. Hope the OP finds out what the problem is with her birds and updates the thread.
Sounds like it is not a problem with lack of grit.
Why were you advised not to give them access to sand? I use sand in the dust bath for my chickens and they are doing fine. If they eat any sand, it is so small it would just go through them in no time. Don't understand the rationale for...
Sorry for your loss. Do your chickens have access to grit? I was expecting to see some grit in the gizzard to help break down the food. I am no expert, but I have been told the chickens can get backed up if they don't have access to grit. If they free range, they probably don't need extra grit...